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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_LegalEntityAxis_lbl" xml:lang="en-US">LegalEntity [Axis]</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NIHGrantRevenueMember_lbl" xml:lang="en-US">NIHGrantRevenueMember</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRevenueArrangementTypeAxis" xlink:to="us-gaap_DeferredRevenueArrangementTypeAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredRevenueArrangementTypeAxis_lbl" xml:lang="en-US">DeferredRevenueArrangementType [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CatoResearchLtdMember" xlink:label="VSTA_CatoResearchLtdMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoResearchLtdMember" xlink:to="VSTA_CatoResearchLtdMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoResearchLtdMember_lbl" xml:lang="en-US">CatoResearchLtdMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNote1Member" xlink:label="VSTA_SeniorNote1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote1Member" xlink:to="VSTA_SeniorNote1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote1Member_lbl" xml:lang="en-US">Senior Note1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xml:lang="en-US">Related Party [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNote2Member" xlink:label="VSTA_SeniorNote2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote2Member" xlink:to="VSTA_SeniorNote2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote2Member_lbl" xml:lang="en-US">Senior Note 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNote3Member" xlink:label="VSTA_SeniorNote3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote3Member" xlink:to="VSTA_SeniorNote3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote3Member_lbl" xml:lang="en-US">Senior Note 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNote5Member" xlink:label="VSTA_SeniorNote5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote5Member" xlink:to="VSTA_SeniorNote5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote5Member_lbl" xml:lang="en-US">Senior Note 5 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xml:lang="en-US">SevenPercentNotesPayableAprilTwoThousandEleven [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:to="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_lbl" xml:lang="en-US">SevenPercentNotesPayableAugustTwoThousandTwelve [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPercentNotesPayableMember" xlink:label="VSTA_SevenPercentNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableMember" xlink:to="VSTA_SevenPercentNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableMember_lbl" xml:lang="en-US">SevenPercentNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CurrentPortionMember" xlink:label="VSTA_CurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionMember" xlink:to="VSTA_CurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionMember_lbl" xml:lang="en-US">CurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:to="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_lbl" xml:lang="en-US">SevenPercentNotesPayableNonCurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BurrPilgerMayerMember" xlink:label="VSTA_BurrPilgerMayerMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BurrPilgerMayerMember_lbl" xml:lang="en-US">BurrPilgerMayer [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DesjardinsMember" xlink:label="VSTA_DesjardinsMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsMember" xlink:to="VSTA_DesjardinsMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DesjardinsMember_lbl" xml:lang="en-US">Desjardins [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_McCarthyTetraultMember" xlink:label="VSTA_McCarthyTetraultMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_McCarthyTetraultMember_lbl" xml:lang="en-US">McCarthyTetrault [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xml:lang="en-US">MayTwoThousandElevenMorrisonFoerster [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_lbl" xml:lang="en-US">AugustTwoThousandTwelveMorrisonAndFoersterNoteA [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_lbl" xml:lang="en-US">AugustTwoThousandTwelveMorrisonAndFoersterNoteB [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountOneMember" xlink:label="VSTA_NoteDiscountOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountOneMember" xlink:to="VSTA_NoteDiscountOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountOneMember_lbl" xml:lang="en-US">NoteDiscountOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPointFivePercentNotesPayableMember" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPointFivePercentNotesPayableMember" xlink:to="VSTA_SevenPointFivePercentNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember_lbl" xml:lang="en-US">SevenPointFivePercentNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CurrentPortionOneMember" xlink:label="VSTA_CurrentPortionOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionOneMember" xlink:to="VSTA_CurrentPortionOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionOneMember_lbl" xml:lang="en-US">CurrentPortionOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NonCurrentPortionAndDiscountMember" xlink:label="VSTA_NonCurrentPortionAndDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountMember" xlink:to="VSTA_NonCurrentPortionAndDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:to="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_lbl" xml:lang="en-US">FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:to="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_lbl" xml:lang="en-US">TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayable [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CurrentPortionTwoMember" xlink:label="VSTA_CurrentPortionTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionTwoMember" xlink:to="VSTA_CurrentPortionTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionTwoMember_lbl" xml:lang="en-US">CurrentPortionTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NonCurrentPortionMember" xlink:label="VSTA_NonCurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionMember" xlink:to="VSTA_NonCurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionMember_lbl" xml:lang="en-US">NonCurrentPortion [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:to="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_lbl" xml:lang="en-US">TenPercentNotesPayableToUnrelatedParties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CurrentPortionThreeMember" xlink:label="VSTA_CurrentPortionThreeMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionThreeMember" xlink:to="VSTA_CurrentPortionThreeMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionThreeMember_lbl" xml:lang="en-US">CurrentPortionThree [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NonCurrentPortionAndDiscountOneMember" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountOneMember" xlink:to="VSTA_NonCurrentPortionAndDiscountOneMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscountOne [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:to="VSTA_SevenPercentNotePayableToCatoHoldingMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember_lbl" xml:lang="en-US">SevenPercentNotePayableToCatoHolding [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountTwoMember" xlink:label="VSTA_NoteDiscountTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountTwoMember" xlink:to="VSTA_NoteDiscountTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountTwoMember_lbl" xml:lang="en-US">NoteDiscountTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableToRelatedPartiesMember" xlink:label="VSTA_NotesPayableToRelatedPartiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableToRelatedPartiesMember" xlink:to="VSTA_NotesPayableToRelatedPartiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_lbl" xml:lang="en-US">NotesPayableToRelatedParties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CurrentPortionFourMember" xlink:label="VSTA_CurrentPortionFourMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionFourMember_lbl" xml:lang="en-US">CurrentPortionFour [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:to="VSTA_NonCurrentPortionAndDiscountTwoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember_lbl" xml:lang="en-US">NonCurrentPortionAndDiscountTwo [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_lbl" xml:lang="en-US">IssuedToPlatinumOnTwoJulyTwoThousandTwelve [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_lbl" xml:lang="en-US">IssuedToPlatinumOnThirtyAugustTwoThousandTwelve [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNotesNonCurrentMember" xlink:label="VSTA_SeniorNotesNonCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNotesNonCurrentMember" xlink:to="VSTA_SeniorNotesNonCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNotesNonCurrentMember_lbl" xml:lang="en-US">SeniorNotesNonCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:to="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_lbl" xml:lang="en-US">FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountMember" xlink:label="VSTA_NoteDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountMember" xlink:to="VSTA_NoteDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountMember_lbl" xml:lang="en-US">Note Discount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:to="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_lbl" xml:lang="en-US">TwelvePercentConvertibleNotesNetNnonCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorNote4Member" xlink:label="VSTA_SeniorNote4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote4Member" xlink:to="VSTA_SeniorNote4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote4Member_lbl" xml:lang="en-US">Senior Note 4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationWarrantsMember" xlink:label="VSTA_ShareBasedCompensationWarrantsMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsMember" xlink:to="VSTA_ShareBasedCompensationWarrantsMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MaximumMember" xlink:to="us-gaap_MaximumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MaximumMember_lbl" xml:lang="en-US">MaximumMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis_lbl" xml:lang="en-US">ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLine [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumMember" xlink:to="us-gaap_MinimumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinimumMember_lbl" xml:lang="en-US">MinimumMember</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="us-gaap_PreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockMember" xlink:to="us-gaap_PreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockMember_lbl" xml:lang="en-US">Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SeriesBPreferredStockMember" xlink:label="us-gaap_SeriesBPreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesBPreferredStockMember" xlink:to="us-gaap_SeriesBPreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesBPreferredStockMember_lbl" xml:lang="en-US">Series B Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeriesB1PreferredStockMember" xlink:label="VSTA_SeriesB1PreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesB1PreferredStockMember" xlink:to="VSTA_SeriesB1PreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesB1PreferredStockMember_lbl" xml:lang="en-US">Series B-1 Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SeriesCPreferredStockMember" xlink:label="us-gaap_SeriesCPreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesCPreferredStockMember" xlink:to="us-gaap_SeriesCPreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesCPreferredStockMember_lbl" xml:lang="en-US">Series C Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockMember" xlink:to="us-gaap_CommonStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockMember_lbl" xml:lang="en-US">Common Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapitalMember" xlink:to="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xml:lang="en-US">Additional Paid-In Capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="us-gaap_TreasuryStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockMember" xlink:to="us-gaap_TreasuryStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockMember_lbl" xml:lang="en-US">Treasury Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesReceivableFromSaleOfStockMember" xlink:label="VSTA_NotesReceivableFromSaleOfStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfStockMember" xlink:to="VSTA_NotesReceivableFromSaleOfStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfStockMember_lbl" xml:lang="en-US">Notes Receivable from Sale of Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember" xlink:label="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember" xlink:to="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember_lbl" xml:lang="en-US">Deficit accumulated during the development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel1Member" xlink:to="us-gaap_FairValueInputsLevel1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xml:lang="en-US">Fair Value, Hierarchy [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel2Member" xlink:to="us-gaap_FairValueInputsLevel2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel3Member" xlink:to="us-gaap_FairValueInputsLevel3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PutOptionNoteTermExtensionLiabilitiesMember" xlink:label="VSTA_PutOptionNoteTermExtensionLiabilitiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PutOptionNoteTermExtensionLiabilitiesMember" xlink:to="VSTA_PutOptionNoteTermExtensionLiabilitiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PutOptionNoteTermExtensionLiabilitiesMember_lbl" xml:lang="en-US">Put Opton Note Term Extension Liabilities [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantLiabilityMember" xlink:label="VSTA_WarrantLiabilityMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantLiabilityMember" xlink:to="VSTA_WarrantLiabilityMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantLiabilityMember_lbl" xml:lang="en-US">Warrant Liability [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeWarrantMember" xlink:label="VSTA_ExchangeWarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeWarrantMember" xlink:to="VSTA_ExchangeWarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeWarrantMember_lbl" xml:lang="en-US">Exchange Warrant [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentAxis_2_lbl" xml:lang="en-US">Debt Instrument [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Oct112012WarrantMember" xlink:label="VSTA_Oct112012WarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Oct112012WarrantMember" xlink:to="VSTA_Oct112012WarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Oct112012WarrantMember_lbl" xml:lang="en-US">Oct 11 2012 Warrant [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Oct192012WarrantMember" xlink:label="VSTA_Oct192012WarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Oct192012WarrantMember" xlink:to="VSTA_Oct192012WarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Oct192012WarrantMember_lbl" xml:lang="en-US">Oct 19 2012 Warrant [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Feb222013WarrantMember" xlink:label="VSTA_Feb222013WarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Feb222013WarrantMember" xlink:to="VSTA_Feb222013WarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Feb222013WarrantMember_lbl" xml:lang="en-US">Feb 22 2013 Warrant [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Mar122013WarrantMember" xlink:label="VSTA_Mar122013WarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Mar122013WarrantMember" xlink:to="VSTA_Mar122013WarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Mar122013WarrantMember_lbl" xml:lang="en-US">March 12 2013 Warrant [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeNoteMember" xlink:label="VSTA_ExchangeNoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeNoteMember" xlink:to="VSTA_ExchangeNoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeNoteMember_lbl" xml:lang="en-US">Exchange Note[Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Oct112012NoteMember" xlink:label="VSTA_Oct112012NoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Oct112012NoteMember" xlink:to="VSTA_Oct112012NoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Oct112012NoteMember_lbl" xml:lang="en-US">Oct 11 2012 Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Oct192012NotetMember" xlink:label="VSTA_Oct192012NotetMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Oct192012NotetMember" xlink:to="VSTA_Oct192012NotetMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Oct192012NotetMember_lbl" xml:lang="en-US">Oct 19 2012 Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Feb222013NoteMember" xlink:label="VSTA_Feb222013NoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Feb222013NoteMember" xlink:to="VSTA_Feb222013NoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Feb222013NoteMember_lbl" xml:lang="en-US">Feb 22 2013 Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Mar122013NoteMember" xlink:label="VSTA_Mar122013NoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Mar122013NoteMember" xlink:to="VSTA_Mar122013NoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Mar122013NoteMember_lbl" xml:lang="en-US">March 12 2013 Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PreModificationPlatinumNoteMember" xlink:label="VSTA_PreModificationPlatinumNoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationPlatinumNoteMember" xlink:to="VSTA_PreModificationPlatinumNoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreModificationPlatinumNoteMember_lbl" xml:lang="en-US">PreModification PlatinumNote [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PostModificationPlatinumNoteMember" xlink:label="VSTA_PostModificationPlatinumNoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationPlatinumNoteMember" xlink:to="VSTA_PostModificationPlatinumNoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostModificationPlatinumNoteMember_lbl" xml:lang="en-US">PostModification PlatinumNote [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationWarrantsTenMember" xlink:label="VSTA_ShareBasedCompensationWarrantsTenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsTenMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsTenMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationWarrantsTwelveMember" xlink:label="VSTA_ShareBasedCompensationWarrantsTwelveMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwelveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwelveMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsTwelveMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsTwelveMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MaximumMember" xlink:to="us-gaap_MaximumMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_MaximumMember_2_lbl" xml:lang="en-US">Maximum [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsByReportLineAxis_2_lbl" xml:lang="en-US">Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumMember" xlink:to="us-gaap_MinimumMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_MinimumMember_2_lbl" xml:lang="en-US">Minimum [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationWarrantsThirteenMember" xlink:label="VSTA_ShareBasedCompensationWarrantsThirteenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsThirteenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsThirteenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsThirteenMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsThirteenMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationWarrantsFourteenMember" xlink:label="VSTA_ShareBasedCompensationWarrantsFourteenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFourteenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFourteenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationWarrantsFourteenMember_lbl" xml:lang="en-US">ShareBasedCompensationWarrantsFourteenMember</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DocumentAndEntityInformationAbstract" xlink:label="VSTA_DocumentAndEntityInformationAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DocumentAndEntityInformationAbstract" xlink:to="VSTA_DocumentAndEntityInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US">Document And Entity Information</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US">Entity Registrant Name</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US">Entity Central Index Key</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentType" xlink:label="dei_DocumentType" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentType_lbl" xml:lang="en-US">Document Type</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentPeriodEndDate_lbl" xml:lang="en-US">Document Period End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_AmendmentFlag_lbl" xml:lang="en-US">Amendment Flag</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xml:lang="en-US">Current Fiscal Year End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityWellKnownSeasonedIssuer" xlink:label="dei_EntityWellKnownSeasonedIssuer" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityWellKnownSeasonedIssuer" xlink:to="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xml:lang="en-US">Is Entity a Well-known Seasoned Issuer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityVoluntaryFilers" xlink:label="dei_EntityVoluntaryFilers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityVoluntaryFilers" xlink:to="dei_EntityVoluntaryFilers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityVoluntaryFilers_lbl" xml:lang="en-US">Is Entity a Voluntary Filer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCurrentReportingStatus" xlink:to="dei_EntityCurrentReportingStatus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCurrentReportingStatus_lbl" xml:lang="en-US">Is Entity's Reporting Status Current?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityFilerCategory_lbl" xml:lang="en-US">Entity Filer Category</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityPublicFloat" xlink:label="dei_EntityPublicFloat" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityPublicFloat" xlink:to="dei_EntityPublicFloat_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityPublicFloat_lbl" xml:lang="en-US">Entity Public Float</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xml:lang="en-US">Entity Common Stock, Shares Outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US">Document Fiscal Period Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2012/dei-2012-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalYearFocus_lbl" xml:lang="en-US">Document Fiscal Year Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:label="us-gaap_StatementOfFinancialPositionAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xml:lang="en-US">Statement of Financial Position [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US">ASSETS</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US">Current assets:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US">Cash and cash equivalents</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ReceivablesNetCurrent" xlink:label="us-gaap_ReceivablesNetCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReceivablesNetCurrent" xlink:to="us-gaap_ReceivablesNetCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ReceivablesNetCurrent_lbl" xml:lang="en-US">Unbilled contract payments receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrent" xlink:to="us-gaap_PrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseCurrent_lbl" xml:lang="en-US">Prepaid expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US">Total current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US">Property and equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US">Total assets</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_LiabilitiesAndStockholdersDeficitAbstract" xlink:label="VSTA_LiabilitiesAndStockholdersDeficitAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LiabilitiesAndStockholdersDeficitAbstract" xlink:to="VSTA_LiabilitiesAndStockholdersDeficitAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LiabilitiesAndStockholdersDeficitAbstract_lbl" xml:lang="en-US">LIABILITIES AND STOCKHOLDERS' DEFICIT</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xml:lang="en-US">Accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xml:lang="en-US">Accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NotesAndLoansPayableCurrent" xlink:label="us-gaap_NotesAndLoansPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesAndLoansPayableCurrent" xlink:to="us-gaap_NotesAndLoansPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesAndLoansPayableCurrent_lbl" xml:lang="en-US">Notes payable and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xml:lang="en-US">Notes payable and accrued interest to related parties</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsCurrent" xlink:label="us-gaap_CapitalLeaseObligationsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsCurrent" xlink:to="us-gaap_CapitalLeaseObligationsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsCurrent_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DeferredRevenues" xlink:label="VSTA_DeferredRevenues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeferredRevenues" xlink:to="VSTA_DeferredRevenues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DeferredRevenues_lbl" xml:lang="en-US">Deferred revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US">Total current liabilities.</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xml:lang="en-US">Non-current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xml:lang="en-US">Senior secured convertible promissory notes, net of discountof $1,963,100 at March 31, 2013 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:to="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_lbl" xml:lang="en-US">Convertible promissory notes, net of discount of $499,300 at March 31, 2012 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableAndAccruedInterest" xlink:label="VSTA_NotesPayableAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterest_lbl" xml:lang="en-US">Notes payable, net of discount of $1,142,600 at March 31, 2013 and $228,900 at March 31, 2012</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xml:lang="en-US">Notes payable to related parties, net of discount of $147,200 at March 31, 2013 and $24,300 at March 31, 2012 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xml:lang="en-US">Warrant liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedOfficersCompensation" xlink:label="VSTA_AccruedOfficersCompensation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedOfficersCompensation" xlink:to="VSTA_AccruedOfficersCompensation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedOfficersCompensation_lbl" xml:lang="en-US">Accrued officers' compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsNoncurrent" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsNoncurrent" xlink:to="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesNoncurrent" xlink:label="us-gaap_LiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesNoncurrent_lbl" xml:lang="en-US">Total non-current liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US">Total liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US">Commitments and contingencies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xml:lang="en-US">Stockholders' deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockValue_lbl" xml:lang="en-US">Preferred stock, $0.001 par value; 10,000,000 shares, including 500,000 Series A shares, authorized at March 31, 2013 and March 31, 2012; 500,000 and 437,055 Series A shares issued and outstanding at March 31, 2013 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US">Common stock, $0.001 par value; 200,000,000 shares authorized at March 31, 2013 and March 31, 2012; 23,480,169 and 18,704,267 shares issued at March 31, 2013 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapital" xlink:to="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xml:lang="en-US">Additional paid-in capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TreasuryStockCarryingBasis" xlink:label="us-gaap_TreasuryStockCarryingBasis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockCarryingBasis" xlink:to="us-gaap_TreasuryStockCarryingBasis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockCarryingBasis_lbl" xml:lang="en-US">Treasury stock, at cost, 2,713,308 and 2,083,858 shares of common stock held at March 31, 2013 and March 31, 2012, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xml:lang="en-US">Notes receivable from sale of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US">Deficit accumulated during development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_StockholdersEquity_lbl" xml:lang="en-US">Total stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US">Total liabilities and stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeniorSecuredConvertibleNotesPayableDiscount" xlink:label="VSTA_SeniorSecuredConvertibleNotesPayableDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertibleNotesPayableDiscount" xlink:to="VSTA_SeniorSecuredConvertibleNotesPayableDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorSecuredConvertibleNotesPayableDiscount_lbl" xml:lang="en-US">Senior secured convertible promissory notes, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableDiscount" xlink:label="VSTA_NotesPayableDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscount_lbl" xml:lang="en-US">Notes payable, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesPayableDiscountRelatedParties" xlink:label="VSTA_NotesPayableDiscountRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscountRelatedParties_lbl" xml:lang="en-US">Notes payable to related parties, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConvertibleNotesDiscount" xlink:label="VSTA_ConvertibleNotesDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNotesDiscount" xlink:to="VSTA_ConvertibleNotesDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertibleNotesDiscount_lbl" xml:lang="en-US">Convertible promissory notes, net of discount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StockholdersEquityAbstract_2_lbl" xml:lang="en-US">Stockholders deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PreferredStockSeriesPerValue1" xlink:label="VSTA_PreferredStockSeriesPerValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesPerValue1_lbl" xml:lang="en-US">Preferred Stock, par value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PreferredStockSeriesASharesAuthorized" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xml:lang="en-US">Preferred Stock, Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PreferredStockSeriesASharesIssued" xlink:label="VSTA_PreferredStockSeriesASharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesIssued_lbl" xml:lang="en-US">PreferredStockSeriesASharesIssued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PreferredStockSeriesASharesOutstanding" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xml:lang="en-US">PreferredStockSeriesASharesOutstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US">Common Stock, Par Value Par Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US">Common Stock, Shares Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US">Common Stock, Shares, Issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="us-gaap_TreasuryStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockShares" xlink:to="us-gaap_TreasuryStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockShares_lbl" xml:lang="en-US">Treasury Stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_IncomeStatementAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xml:lang="en-US">Income Statement [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_RevenuesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenuesAbstract_lbl" xml:lang="en-US">Revenues:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RevenueFromGrants" xlink:label="us-gaap_RevenueFromGrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromGrants" xlink:to="us-gaap_RevenueFromGrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueFromGrants_lbl" xml:lang="en-US">Grant revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RevenueFromExternalCustomers" xlink:label="VSTA_RevenueFromExternalCustomers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RevenueFromExternalCustomers_lbl" xml:lang="en-US">Collaboration revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherSalesRevenueNet" xlink:label="us-gaap_OtherSalesRevenueNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherSalesRevenueNet" xlink:to="us-gaap_OtherSalesRevenueNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherSalesRevenueNet_lbl" xml:lang="en-US">Other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Revenues_lbl" xml:lang="en-US">Total revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="us-gaap_OperatingExpensesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xml:lang="en-US">Operating expenses:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xml:lang="en-US">Research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AcquiredInProcessResearchAndDevelopment" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AcquiredInProcessResearchAndDevelopment" xlink:to="VSTA_AcquiredInProcessResearchAndDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment_lbl" xml:lang="en-US">Acquired in-process research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpense" xlink:to="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xml:lang="en-US">General and administrative</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingExpenses_lbl" xml:lang="en-US">Total operating expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US">Loss from operations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xml:lang="en-US">Other expenses, net:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestExpense" xlink:to="us-gaap_InterestExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestExpense_lbl" xml:lang="en-US">Interest expense, net</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in put and note extension option and warrant liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:to="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherIncome" xlink:label="us-gaap_OtherIncome" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherIncome" xlink:to="us-gaap_OtherIncome_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherIncome_lbl" xml:lang="en-US">Other income</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xml:lang="en-US">Loss before income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetIncomeLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DeemedDividendOnSeriesPreferredStock" xlink:label="VSTA_DeemedDividendOnSeriesPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeemedDividendOnSeriesPreferredStock" xlink:to="VSTA_DeemedDividendOnSeriesPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DeemedDividendOnSeriesPreferredStock_lbl" xml:lang="en-US">Deemed dividend on Series A Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetLossAttributableToCommonStockholders" xlink:label="VSTA_NetLossAttributableToCommonStockholders" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetLossAttributableToCommonStockholders" xlink:to="VSTA_NetLossAttributableToCommonStockholders_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetLossAttributableToCommonStockholders_lbl" xml:lang="en-US">Net loss attributable to common stockholders</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareDiluted" xlink:to="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xml:lang="en-US">Basic and diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xml:lang="en-US">Weighted average shares used in computing basic and diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ComprehensiveLoss" xlink:label="VSTA_ComprehensiveLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComprehensiveLoss" xlink:to="VSTA_ComprehensiveLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComprehensiveLoss_lbl" xml:lang="en-US">Comprehensive loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProfitLoss" xlink:to="us-gaap_ProfitLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationAndAmortization" xlink:to="us-gaap_DepreciationAndAmortization_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xml:lang="en-US">Depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:to="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_lbl" xml:lang="en-US">Amortization of imputed discount on non-interest bearing notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:to="VSTA_AmortizationOfDiscountsOn77.5And10Notes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes_lbl" xml:lang="en-US">Amortization of discounts on 7%, 7.5% and 10% notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:to="VSTA_AmortizationOfDiscountsOnPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes_lbl" xml:lang="en-US">Amortization of discounts on Platinum notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:to="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_lbl" xml:lang="en-US">Amortization of discounts on August 2010 short-term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:to="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Amortization of discounts on February 2012 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_LossOnSettlementsOfAccountsPayable" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xml:lang="en-US">Loss on settlements of accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in warrant and put and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US">Stock-based compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpenseRelatedToModificationOfWarrants" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xml:lang="en-US">Expense related to modification of warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:to="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xml:lang="en-US">Fair value of Series C preferred stock, common stock, and warrants granted for services prior to the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfCommonStockGrantedForServicesPriorToMerger" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesPriorToMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesPriorToMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesPriorToMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesPriorToMerger_lbl" xml:lang="en-US">Fair value of common stock granted for services prior to the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of common stock granted for services following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of warrants granted for services following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xml:lang="en-US">Fair value of additional warrants granted pursuant to exercises of modified warrants (fiscal year 2013) and under Discounted Warrant Exercise Program (fiscal year 2012)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xml:lang="en-US">Fair value of common stock issued for note term modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InterestIncomeOnNoteReceivableForStockPurchase" xlink:label="VSTA_InterestIncomeOnNoteReceivableForStockPurchase" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InterestIncomeOnNoteReceivableForStockPurchase" xlink:to="VSTA_InterestIncomeOnNoteReceivableForStockPurchase_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InterestIncomeOnNoteReceivableForStockPurchase_lbl" xml:lang="en-US">Interest income on note receivable for stock purchase</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xml:lang="en-US">Consulting services by related parties settled by issuing promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:to="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xml:lang="en-US">Gain on sale of assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xml:lang="en-US">Changes in operating assets and liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xml:lang="en-US">Unbilled contract payments receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xml:lang="en-US">Prepaid expenses and other current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xml:lang="en-US">Accounts payable and accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xml:lang="en-US">Deferred revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xml:lang="en-US">Net cash used in operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from investing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:to="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xml:lang="en-US">Purchases of equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xml:lang="en-US">Net cash used in investing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from financing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xml:lang="en-US">Net proceeds from issuance of common stock and warrants, including units</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:label="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock" xlink:to="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock_lbl" xml:lang="en-US">Net proceeds from issuance of preferred stock and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xml:lang="en-US">Proceeds from exercise of modified warrants (fiscal 2013) and under Discounted Warrant Exercise Program (fiscal 2012)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ProceedsFromUnsecuredLinesOfCredit" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit_lbl" xml:lang="en-US">Proceeds from issuance of notes under line of credit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_lbl" xml:lang="en-US">Proceeds from issuance of 7% note payable to founding stockholder</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xml:lang="en-US">Net proceeds from issuance of 7% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 10% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of Platinum notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 2008/2010 notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 2006/2007 notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:to="VSTA_ProceedsFromIssuanceOf7NotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable_lbl" xml:lang="en-US">Proceeds from issuance of 7% notes payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of August 2010 short-term notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of February 2012 12% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xml:lang="en-US">Repayment of capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfNotesPayable" xlink:to="us-gaap_RepaymentsOfNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfNotesPayable_lbl" xml:lang="en-US">Repayment of notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xml:lang="en-US">Net cash provided by financing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US">Net increase in cash and cash equivalents</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xml:lang="en-US">Cash and cash equivalents at beginning of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xml:lang="en-US">Cash and cash equivalents at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xml:lang="en-US">Supplemental disclosure of cash flow activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestPaid" xlink:label="us-gaap_InterestPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPaid" xlink:to="us-gaap_InterestPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestPaid_lbl" xml:lang="en-US">Cash paid for interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeTaxesPaid" xlink:label="us-gaap_IncomeTaxesPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxesPaid" xlink:to="us-gaap_IncomeTaxesPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxesPaid_lbl" xml:lang="en-US">Cash paid for income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xml:lang="en-US">Supplemental disclosure of noncash activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity_lbl" xml:lang="en-US">Forgiveness of accrued compensation and accrued interest payable to officers transferred to equity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" xlink:label="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" xlink:to="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation_lbl" xml:lang="en-US">Exercise of warrants and options in exchange for debt cancellation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" xlink:label="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" xlink:to="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock_lbl" xml:lang="en-US">Settlement of accrued and prepaid interest by issuance of Series C Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesCPreferredStock" xlink:label="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesCPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesCPreferredStock" xlink:to="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesCPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesCPreferredStock_lbl" xml:lang="en-US">Conversion of 10% notes payable, net of discount, and related accrued interest into Series C Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" xlink:label="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" xlink:to="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment_lbl" xml:lang="en-US">Issuance of Series B-1 Preferred stock for acquired in-process research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOf7NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesBPreferredStock" xlink:label="VSTA_ConversionOf7NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesBPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf7NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesBPreferredStock" xlink:to="VSTA_ConversionOf7NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesBPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf7NotesPayableNetOfDiscountAndRelatedAccruedInterestIntoSeriesBPreferredStock_lbl" xml:lang="en-US">Conversion of 7% notes payable, net of discount, and related accrued interest into Series B Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccountsPayableIntoConvertiblePromissoryNotes" xlink:label="VSTA_ConversionOfAccountsPayableIntoConvertiblePromissoryNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableIntoConvertiblePromissoryNotes" xlink:to="VSTA_ConversionOfAccountsPayableIntoConvertiblePromissoryNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableIntoConvertiblePromissoryNotes_lbl" xml:lang="en-US">Conversion of accounts payable into convertible promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccountsPayableIntoNotePayable" xlink:label="VSTA_ConversionOfAccountsPayableIntoNotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableIntoNotePayable" xlink:to="VSTA_ConversionOfAccountsPayableIntoNotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableIntoNotePayable_lbl" xml:lang="en-US">Conversion of accounts payable into note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccountsPayableIntoCommonStock" xlink:label="VSTA_ConversionOfAccountsPayableIntoCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableIntoCommonStock" xlink:to="VSTA_ConversionOfAccountsPayableIntoCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableIntoCommonStock_lbl" xml:lang="en-US">Conversion of accounts payable into common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" xlink:label="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" xlink:to="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock_lbl" xml:lang="en-US">Conversion of accrued interest on convertible promissory notes into common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants_lbl" xml:lang="en-US">Notes receivable from sale of common stock to related parties upon exercise of options and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsIncurred" xlink:label="us-gaap_CapitalLeaseObligationsIncurred" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsIncurred" xlink:to="us-gaap_CapitalLeaseObligationsIncurred_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsIncurred_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfPlatinumNotes" xlink:label="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfPlatinumNotes" xlink:to="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfPlatinumNotes_lbl" xml:lang="en-US">Recognition of put option and note term extension option liabilities upon issuance of Platinum Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" xlink:label="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" xlink:to="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications_lbl" xml:lang="en-US">Incremental fair value of put option and note term extension option liabilities from debt modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification_lbl" xml:lang="en-US">Incremental fair value of note conversion option from debt modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalFairValueOfWarrantFromDebtModifications" xlink:label="VSTA_IncrementalFairValueOfWarrantFromDebtModifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfWarrantFromDebtModifications" xlink:to="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_lbl" xml:lang="en-US">Incremental fair value of warrant from debt modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" xlink:to="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_lbl" xml:lang="en-US">Recognition of warrant liability upon adoption of new accounting standard</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_lbl" xml:lang="en-US">Fair value of warrants issued with August 2010 short term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes" xlink:label="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes_lbl" xml:lang="en-US">Note Discount upon issuance of August 2010 short-term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Fair value of warrants issued with February 2012 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" xlink:label="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Note Discount upon issuance of February 2012 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccruedInterestOn20062007And20082010NotesIntoCommonStock" xlink:label="VSTA_ConversionOfAccruedInterestOn20062007And20082010NotesIntoCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestOn20062007And20082010NotesIntoCommonStock" xlink:to="VSTA_ConversionOfAccruedInterestOn20062007And20082010NotesIntoCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestOn20062007And20082010NotesIntoCommonStock_lbl" xml:lang="en-US">Conversion of 2006/2007 and 2008/2010 Notes into Units, including accrued interest of $1,365,600</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" xlink:label="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" xlink:to="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits_lbl" xml:lang="en-US">Conversion of all series of pre-Merger preferred stock into Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccruedInterestOn2011PlatinumNoteIntoSeriesPreferredStock" xlink:label="VSTA_ConversionOfAccruedInterestOn2011PlatinumNoteIntoSeriesPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestOn2011PlatinumNoteIntoSeriesPreferredStock" xlink:to="VSTA_ConversionOfAccruedInterestOn2011PlatinumNoteIntoSeriesPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestOn2011PlatinumNoteIntoSeriesPreferredStock_lbl" xml:lang="en-US">Conversion of 2011 Platinum Note into Series A Preferred stock, including accrued interest of $611,100 and conversion premium</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccruedInterestOnAugust2010NoteInto7NotePayable" xlink:label="VSTA_ConversionOfAccruedInterestOnAugust2010NoteInto7NotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestOnAugust2010NoteInto7NotePayable" xlink:to="VSTA_ConversionOfAccruedInterestOnAugust2010NoteInto7NotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestOnAugust2010NoteInto7NotePayable_lbl" xml:lang="en-US">Conversion of 7% note payable and accrued interest of $11,500 into common stock and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" xlink:label="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" xlink:to="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable_lbl" xml:lang="en-US">Conversion of accounts payable to Morrison &amp; Foerster, McCarthy Tetrault and Desjardins into notes payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" xlink:label="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" xlink:to="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits_lbl" xml:lang="en-US">Accounts payable and cancellation premium converted into 2011 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" xlink:label="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" xlink:to="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable_lbl" xml:lang="en-US">Accrued interest on Cato Holding Company note converted to note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" xlink:label="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" xlink:to="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises_lbl" xml:lang="en-US">Accounts payable settled in December 2011 and May/June 2012 warrant exercises</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InsurancePremiumsSettledByIssuingNotePayable" xlink:label="VSTA_InsurancePremiumsSettledByIssuingNotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InsurancePremiumsSettledByIssuingNotePayable" xlink:to="VSTA_InsurancePremiumsSettledByIssuingNotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InsurancePremiumsSettledByIssuingNotePayable_lbl" xml:lang="en-US">Insurance premiums settled by issuing note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" xlink:label="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" xlink:to="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits_lbl" xml:lang="en-US">Conversion of accrued interest and fees on February 2012 Notes into 2012 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" xlink:label="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" xlink:to="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote_lbl" xml:lang="en-US">Accrued interest on July and August 2012 Notes to Platinum converted into Exchange Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" xlink:label="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" xlink:to="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock_lbl" xml:lang="en-US">Accounts payable settled by issuance of stock or notes payable and stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" xlink:label="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" xlink:to="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits_lbl" xml:lang="en-US">Accounts payable converted into 2012 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RecognitionOfWarrantLiabilityUponIssuance" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityUponIssuance" xlink:to="VSTA_RecognitionOfWarrantLiabilityUponIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponIssuance_lbl" xml:lang="en-US">Recognition of warrant liability upon issuance to Platinum of October 2012 Exchange Note and October 2012, February 2013 and March 2013 Investment Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RecognitionOfWarrantLiabilityForPotentialIssuance" xlink:label="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuance" xlink:to="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuance_lbl" xml:lang="en-US">Recognition of warrant liability for potential issuance to Platinum of Series A Exchange Warrant under the terms of the October 2012 Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementTable_lbl" xml:lang="en-US">Statement [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementLineItems_lbl" xml:lang="en-US">Statement [Line Items]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockholdersEquityForPreferredStock" xlink:label="VSTA_StockholdersEquityForPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="VSTA_StockholdersEquityForPreferredStock_lbl" xml:lang="en-US">Beginning Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SharesIssuedForPreferredStock" xlink:label="VSTA_SharesIssuedForPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="VSTA_SharesIssuedForPreferredStock_lbl" xml:lang="en-US">Beginning Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $24,000, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $24,000, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $5,500, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $5,500, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, including conversion of $575,000 face value of 7% convertible notes plus accrued interest of $3,800, net of unamortized discount of $70,800 and issuance costs of $39,800, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, including conversion of $575,000 face value of 7% convertible notes plus accrued interest of $3,800, net of unamortized discount of $70,800 and issuance costs of $39,800, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount" xlink:to="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, net of issuance costs of $97,200, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares" xlink:to="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, net of issuance costs of $97,200, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_lbl" xml:lang="en-US">Issuance of Series B-1 preferred stock at $5.545 for acquired in-process research and development, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_lbl" xml:lang="en-US">Issuance of Series B-1 preferred stock at $5.545 for acquired in-process research and development, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, including conversion of $1,655,000 face value of 10% convertible notes plus accrued interest of $408,600, net of unamortized note discount of $13,200 and issuance costs of $27,200, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, including conversion of $1,655,000 face value of 10% convertible notes plus accrued interest of $408,600, net of unamortized note discount of $13,200 and issuance costs of $27,200, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Series C preferred stock, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Series C preferred stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, net of issuance costs of $20,700, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, net of issuance costs of $20,700, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for services and in payment of interest on line of credit, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for services and in payment of interest on line of credit, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_lbl" xml:lang="en-US">Conversion of all series of preferred stock into VistaGen common stock in connection with the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_lbl" xml:lang="en-US">Conversion of all series of preferred stock into VistaGen common stock in connection with the Merger, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="VSTA_StockholdersEquityForPreferredStock_2_lbl" xml:lang="en-US">Ending Balance, Amount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="VSTA_SharesIssuedForPreferredStock_2_lbl" xml:lang="en-US">Ending Balance, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_StockholdersEquity_2_lbl" xml:lang="en-US">Beginning Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SharesIssued" xlink:label="us-gaap_SharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_SharesIssued_lbl" xml:lang="en-US">Beginning Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InitialSaleOfCommonStockForCashToFounderAmount" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InitialSaleOfCommonStockForCashToFounderAmount" xlink:to="VSTA_InitialSaleOfCommonStockForCashToFounderAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderAmount_lbl" xml:lang="en-US">Initial sale of common stock for cash to Founder, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InitialSaleOfCommonStockForCashToFounderShares" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InitialSaleOfCommonStockForCashToFounderShares" xlink:to="VSTA_InitialSaleOfCommonStockForCashToFounderShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderShares_lbl" xml:lang="en-US">Initial sale of common stock for cash to Founder, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfCommonStockIssuedForServicesAmount" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForServicesAmount" xlink:to="VSTA_FairValueOfCommonStockIssuedForServicesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesAmount_lbl" xml:lang="en-US">Fair value of common stock issued for services, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfCommonStockIssuedForServicesShares" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForServicesShares" xlink:to="VSTA_FairValueOfCommonStockIssuedForServicesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesShares_lbl" xml:lang="en-US">Fair value of common stock issued for services, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_EffectOfMergerAmount" xlink:label="VSTA_EffectOfMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerAmount" xlink:to="VSTA_EffectOfMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfMergerAmount_lbl" xml:lang="en-US">Effect of the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_EffectOfMergerShares" xlink:label="VSTA_EffectOfMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerShares" xlink:to="VSTA_EffectOfMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfMergerShares_lbl" xml:lang="en-US">Effect of the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SaleOfCommonStockForCashAmount" xlink:label="VSTA_SaleOfCommonStockForCashAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashAmount" xlink:to="VSTA_SaleOfCommonStockForCashAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfCommonStockForCashAmount_lbl" xml:lang="en-US">Sale of common stock for cash, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SaleOfCommonStockForCashShares" xlink:label="VSTA_SaleOfCommonStockForCashShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashShares" xlink:to="VSTA_SaleOfCommonStockForCashShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfCommonStockForCashShares_lbl" xml:lang="en-US">Sale of common stock for cash, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedForServices" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServices" xlink:to="VSTA_FairValueOfWarrantsIssuedForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices_lbl" xml:lang="en-US">Fair value of warrants issued for services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with 7% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with 10% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Series C Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Cash, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Cash, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Debt cancellation, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Debt cancellation, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Notes receivable, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan and warrants for: Notes receivable, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SharebasedCompensationExpense" xlink:label="VSTA_SharebasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharebasedCompensationExpense" xlink:to="VSTA_SharebasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharebasedCompensationExpense_lbl" xml:lang="en-US">Share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_lbl" xml:lang="en-US">Forgiveness of accrued compensation and accrued interest payable to officers</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount" xlink:to="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount_lbl" xml:lang="en-US">Common stock issued upon settlement of employment contract, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares" xlink:to="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares_lbl" xml:lang="en-US">Common stock issued upon settlement of employment contract, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Platinum Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedInterestOnNotesReceivable" xlink:label="VSTA_AccruedInterestOnNotesReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnNotesReceivable" xlink:to="VSTA_AccruedInterestOnNotesReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnNotesReceivable_lbl" xml:lang="en-US">Accrued interest on notes receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 2008 Stock Incentive Plan and Scientific Advisory Plan, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 2008 Stock Incentive Plan and Scientific Advisory Plan, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Platinum Notes and incremental fair value of warrant modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_EffectOfReverseStockSplit" xlink:label="VSTA_EffectOfReverseStockSplit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfReverseStockSplit" xlink:to="VSTA_EffectOfReverseStockSplit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfReverseStockSplit_lbl" xml:lang="en-US">Effect of reverse stock split</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:to="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_lbl" xml:lang="en-US">Cumulative effect of adopting new accounting standard</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfWarrantAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfWarrantAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfWarrantAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of warrant, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedUponExerciseOfWarrantShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfWarrantShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfWarrantShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantShares_lbl" xml:lang="en-US">Common stock issued upon exercise of warrant, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_lbl" xml:lang="en-US">Common stock issued for cancellation of accounts payable and accrued interest, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_lbl" xml:lang="en-US">Common stock issued for cancellation of accounts payable and accrued interest, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_lbl" xml:lang="en-US">Incremental fair value of note conversion options from debt modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedForServicesAmount" xlink:label="VSTA_CommonStockIssuedForServicesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForServicesAmount" xlink:to="VSTA_CommonStockIssuedForServicesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForServicesAmount_lbl" xml:lang="en-US">Common stock issued for services, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockIssuedForServicesShares" xlink:label="VSTA_CommonStockIssuedForServicesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForServicesShares" xlink:to="VSTA_CommonStockIssuedForServicesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForServicesShares_lbl" xml:lang="en-US">Common stock issued for services, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification" xlink:label="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification_lbl" xml:lang="en-US">Fair value of warrants issued for services and incremental fair value of warrant modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes_lbl" xml:lang="en-US">Fair value of warrants issued in connection with 7.5% Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes_lbl" xml:lang="en-US">Fair value of warrants issued in connection with the August 2010 Short-Term Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ReclassificationOfWarrantLiabilityToEquity" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReclassificationOfWarrantLiabilityToEquity" xlink:to="VSTA_ReclassificationOfWarrantLiabilityToEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity_lbl" xml:lang="en-US">Reclassification of warrant liability to equity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalValueOfPlatinumNoteModification" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfPlatinumNoteModification" xlink:to="VSTA_IncrementalValueOfPlatinumNoteModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification_lbl" xml:lang="en-US">Incremental value of Platinum note modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" xlink:to="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_lbl" xml:lang="en-US">Incremental value of Morrison Foerster warrant modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_lbl" xml:lang="en-US">Stock issued in May 2011 Private Placement, net of $202,000 placement fees, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_lbl" xml:lang="en-US">Stock issued in May 2011 Private Placement, net of $202,000 placement fees, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PaymentsOnNoteReceivableForSaleOfStock" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PaymentsOnNoteReceivableForSaleOfStock" xlink:to="VSTA_PaymentsOnNoteReceivableForSaleOfStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock_lbl" xml:lang="en-US">Payments on note receivable for sale of stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_lbl" xml:lang="en-US">Stock issued upon conversion of convertible promissory notes, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_lbl" xml:lang="en-US">Stock issued upon conversion of convertible promissory notes, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_lbl" xml:lang="en-US">Stock issued upon conversion of all series of preferred stock, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_lbl" xml:lang="en-US">Stock issued upon conversion of all series of preferred stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_lbl" xml:lang="en-US">Fair value of stock issued for services prior to the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_lbl" xml:lang="en-US">Fair value of stock issued for services prior to the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ForgivenessOfNotesAtTheMergerAmount" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfNotesAtTheMergerAmount" xlink:to="VSTA_ForgivenessOfNotesAtTheMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount_lbl" xml:lang="en-US">Forgiveness of notes at the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ForgivenessOfNotesAtTheMergerShares" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfNotesAtTheMergerShares" xlink:to="VSTA_ForgivenessOfNotesAtTheMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerShares_lbl" xml:lang="en-US">Forgiveness of notes at the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_lbl" xml:lang="en-US">Stock issued upon exercise of modified warrants (includes Platinum exercises), Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_lbl" xml:lang="en-US">Stock issued upon exercise of modified warrants (includes Platinum exercises), Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" xlink:label="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" xlink:to="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_lbl" xml:lang="en-US">Incremental value of warrant modifications (including modification of Platinum warrants)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_lbl" xml:lang="en-US">Fair value of bonus warrants under Discounted Warrant Exercise Program</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInFall2011FollowonOfferingAmount" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingAmount" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingAmount_lbl" xml:lang="en-US">Stock issued in Fall 2011 Follow-on Offering, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInFall2011FollowonOfferingShares" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingShares" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingShares_lbl" xml:lang="en-US">Stock issued in Fall 2011 Follow-on Offering, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xml:lang="en-US">Stock issued upon exercise of options from 1999 Stock Incentive Plan, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xml:lang="en-US">Stock issued upon exercise of options from 1999 Stock Incentive Plan, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_lbl" xml:lang="en-US">Fair value of stock issued for services following the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_lbl" xml:lang="en-US">Fair value of stock issued for services following the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PlacementFeesOn12ConvertibleNotes" xlink:label="VSTA_PlacementFeesOn12ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlacementFeesOn12ConvertibleNotes" xlink:to="VSTA_PlacementFeesOn12ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlacementFeesOn12ConvertibleNotes_lbl" xml:lang="en-US">Placement fees on 12% Convertible Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued and beneficial conversion feature in connection with 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_lbl" xml:lang="en-US">Stock issued in connection with note term extension, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_lbl" xml:lang="en-US">Stock issued in connection with note term extension, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_lbl" xml:lang="en-US">Stock issued upon conversion of Platinum Note to equity (net of Platinum warrant exercise reflected above), Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_lbl" xml:lang="en-US">Stock issued upon conversion of Platinum Note to equity (net of Platinum warrant exercise reflected above), Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Common Stock Exchange Agreement, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Common Stock Exchange Agreement, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Note and Warrant Exchange Agreement, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Note and Warrant Exchange Agreement, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" xlink:label="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" xlink:to="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants_lbl" xml:lang="en-US">Fair value of warrants issued upon exercise of modified warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" xlink:to="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable_lbl" xml:lang="en-US">Fair value of shares issued in settlement of accounts payable, amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" xlink:to="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares_lbl" xml:lang="en-US">Fair value of shares issued in settlement of accounts payable, shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ModificationOfNoteReceivableFromSaleOfStock" xlink:label="VSTA_ModificationOfNoteReceivableFromSaleOfStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ModificationOfNoteReceivableFromSaleOfStock" xlink:to="VSTA_ModificationOfNoteReceivableFromSaleOfStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ModificationOfNoteReceivableFromSaleOfStock_lbl" xml:lang="en-US">Modification of note receivable from sale of stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to Cato Holding Company in connection with note payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to Cato Holding Company in connection with accounts payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to University Health Network in connection with accounts payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes_lbl" xml:lang="en-US">Fair value of warrants issued to Morrison &amp; Foerster, Cato Reearch Ltd. and University Health Network in connection with accrued interest on underlying notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount" xlink:to="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount_lbl" xml:lang="en-US">Sale of Units in Winter 2012 Private Placement, net, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares" xlink:to="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares_lbl" xml:lang="en-US">Sale of Units in Winter 2012 Private Placement, net, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeOfFebruary2012ConvertibleNotesAmount" xlink:label="VSTA_ExchangeOfFebruary2012ConvertibleNotesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeOfFebruary2012ConvertibleNotesAmount" xlink:to="VSTA_ExchangeOfFebruary2012ConvertibleNotesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeOfFebruary2012ConvertibleNotesAmount_lbl" xml:lang="en-US">Exchange of February 2012 convertible notes, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeOfFebruary2012ConvertibleNotesShares" xlink:label="VSTA_ExchangeOfFebruary2012ConvertibleNotesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeOfFebruary2012ConvertibleNotesShares" xlink:to="VSTA_ExchangeOfFebruary2012ConvertibleNotesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeOfFebruary2012ConvertibleNotesShares_lbl" xml:lang="en-US">Exchange of February 2012 convertible notes, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes_lbl" xml:lang="en-US">Fair value of warrants issued to banker in connection with exchange of February 2012 convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" xlink:label="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" xlink:to="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum_lbl" xml:lang="en-US">Premium of fair value over face value of Exchange Note issued to PLatinum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncreaseDecreaseInDerivativeLiabilities" xlink:label="us-gaap_IncreaseDecreaseInDerivativeLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDerivativeLiabilities" xlink:to="us-gaap_IncreaseDecreaseInDerivativeLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDerivativeLiabilities_lbl" xml:lang="en-US">Fair value of Series A Exchange Warrant issuable to Platinum recorded as a Warrant Liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013" xlink:label="VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013" xlink:to="VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013_lbl" xml:lang="en-US">Proceeds allocated to beneficial conversion feature of Investment Notes issued to PLatinum in October 2012, February 2013 and March 2013</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" xlink:label="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" xlink:to="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013_lbl" xml:lang="en-US">Incremental fair value of warrant modifications in Feburary 2013</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLoss_2_lbl" xml:lang="en-US">Net Loss</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_StockholdersEquity_3_lbl" xml:lang="en-US">Ending Balance, Amount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_SharesIssued_2_lbl" xml:lang="en-US">Ending Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NotesToFinancialStatementsAbstract" xlink:label="VSTA_NotesToFinancialStatementsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesToFinancialStatementsAbstract" xlink:to="VSTA_NotesToFinancialStatementsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesToFinancialStatementsAbstract_lbl" xml:lang="en-US">Notes to Financial Statements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_HistoryAndOrganizationTextBlock" xlink:label="VSTA_HistoryAndOrganizationTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_HistoryAndOrganizationTextBlock_lbl" xml:lang="en-US">Description of Business</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" xml:lang="en-US">Research and Development Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CompensationRelatedCostsPolicyTextBlock" xlink:label="us-gaap_CompensationRelatedCostsPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CompensationRelatedCostsPolicyTextBlock" xlink:to="us-gaap_CompensationRelatedCostsPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CompensationRelatedCostsPolicyTextBlock_lbl" xml:lang="en-US">Share-Based Compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_IncomeTaxPolicyTextBlock" xlink:label="us-gaap_IncomeTaxPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxPolicyTextBlock" xlink:to="us-gaap_IncomeTaxPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_lbl" xml:lang="en-US">Income Taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ConcentrationRiskCreditRisk" xlink:label="us-gaap_ConcentrationRiskCreditRisk" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskCreditRisk" xlink:to="us-gaap_ConcentrationRiskCreditRisk_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskCreditRisk_lbl" xml:lang="en-US">Concentrations of Credit Risk</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:to="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xml:lang="en-US">Comprehensive Loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EarningsPerSharePolicyTextBlock" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerSharePolicyTextBlock" xlink:to="us-gaap_EarningsPerSharePolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock_lbl" xml:lang="en-US">Loss per Common Share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RecentlyAdoptedAccountingStandardsPolicyTextBlock" xlink:label="VSTA_RecentlyAdoptedAccountingStandardsPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecentlyAdoptedAccountingStandardsPolicyTextBlock" xlink:to="VSTA_RecentlyAdoptedAccountingStandardsPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecentlyAdoptedAccountingStandardsPolicyTextBlock_lbl" xml:lang="en-US">Recently Adopted Accounting Standards</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xml:lang="en-US">Recent Accounting Pronouncements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesTablesAbstract_lbl" xml:lang="en-US">Summary Of Significant Accounting Policies Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xml:lang="en-US">Earning Per Share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FiarValueMeasurementsTablesAbstract" xlink:label="VSTA_FiarValueMeasurementsTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FiarValueMeasurementsTablesAbstract" xlink:to="VSTA_FiarValueMeasurementsTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FiarValueMeasurementsTablesAbstract_lbl" xml:lang="en-US">Fair Value Measurements Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_lbl" xml:lang="en-US">Fair value heirarchy for liabilities measured at fair value on a recurring basis</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ChangesInLevel3Liabilities" xlink:label="VSTA_ChangesInLevel3Liabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangesInLevel3Liabilities" xlink:to="VSTA_ChangesInLevel3Liabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangesInLevel3Liabilities_lbl" xml:lang="en-US">Changes in Level 3 liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xml:lang="en-US">Property and equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedExpensesTablesAbstract" xlink:label="VSTA_AccruedExpensesTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesTablesAbstract" xlink:to="VSTA_AccruedExpensesTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedExpensesTablesAbstract_lbl" xml:lang="en-US">Accrued Expenses Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" xlink:to="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract_lbl" xml:lang="en-US">Convertible Promissory Notes And Other Notes Payable Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" xlink:to="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_lbl" xml:lang="en-US">Convertible Promissory Notes and Other Notes Payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeWarrantAndInvestmentWarrantsTableTextBlock" xlink:label="VSTA_ExchangeWarrantAndInvestmentWarrantsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeWarrantAndInvestmentWarrantsTableTextBlock" xlink:to="VSTA_ExchangeWarrantAndInvestmentWarrantsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeWarrantAndInvestmentWarrantsTableTextBlock_lbl" xml:lang="en-US">Exchange Warrant and Investment Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NoteDiscountAndEffectiveInterestRateTableTextBlock" xlink:label="VSTA_NoteDiscountAndEffectiveInterestRateTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountAndEffectiveInterestRateTableTextBlock" xlink:to="VSTA_NoteDiscountAndEffectiveInterestRateTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountAndEffectiveInterestRateTableTextBlock_lbl" xml:lang="en-US">Components of note discount and effective interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncrementalValueOfAmendedMfWarrant" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfAmendedMfWarrant" xlink:to="VSTA_IncrementalValueOfAmendedMfWarrant_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant_lbl" xml:lang="en-US">Amended M&amp;F Warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CapitalStockTablesAbstract" xlink:label="VSTA_CapitalStockTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockTablesAbstract" xlink:to="VSTA_CapitalStockTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockTablesAbstract_lbl" xml:lang="en-US">Capital Stock Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Option Pricing Model</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BlackscholesOptionPricingModelModificationsTableTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelModificationsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelModificationsTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelModificationsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelModificationsTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Option Pricing Model on Modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BlackscholesOptionPricingModelOnAssumptionsTableTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelOnAssumptionsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelOnAssumptionsTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelOnAssumptionsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelOnAssumptionsTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Option Pricing Model on Assumptions</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OtherWarrantModificationsAssumptionsTableTextBlock" xlink:label="VSTA_OtherWarrantModificationsAssumptionsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OtherWarrantModificationsAssumptionsTableTextBlock" xlink:to="VSTA_OtherWarrantModificationsAssumptionsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OtherWarrantModificationsAssumptionsTableTextBlock_lbl" xml:lang="en-US">Other Warrant Modifications assumptions</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BlackscholesOtherWarrantModificationsOptionPricingModelOnAssumptionsTableTextBlock" xlink:label="VSTA_BlackscholesOtherWarrantModificationsOptionPricingModelOnAssumptionsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOtherWarrantModificationsOptionPricingModelOnAssumptionsTableTextBlock" xlink:to="VSTA_BlackscholesOtherWarrantModificationsOptionPricingModelOnAssumptionsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOtherWarrantModificationsOptionPricingModelOnAssumptionsTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Other Warrant Modifications Option Pricing Model on Assumptions</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TemporaryEquityTableTextBlock" xlink:label="us-gaap_TemporaryEquityTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityTableTextBlock" xlink:to="us-gaap_TemporaryEquityTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TemporaryEquityTableTextBlock_lbl" xml:lang="en-US">Warrants outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ReservedSharesTableTextBlock" xlink:label="VSTA_ReservedSharesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReservedSharesTableTextBlock" xlink:to="VSTA_ReservedSharesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ReservedSharesTableTextBlock_lbl" xml:lang="en-US">Reserved Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:to="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xml:lang="en-US">Provision/benefit computed for income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xml:lang="en-US">Components of deferred tax assets</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" xlink:label="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" xlink:to="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_lbl" xml:lang="en-US">Share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock_lbl" xml:lang="en-US">Black-Scholes option valuation model assumptions for share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockOptionActivitySummaryTextBlock" xlink:label="VSTA_StockOptionActivitySummaryTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockOptionActivitySummaryTextBlock" xlink:to="VSTA_StockOptionActivitySummaryTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockOptionActivitySummaryTextBlock_lbl" xml:lang="en-US">Summary of stock option plan activity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" xlink:label="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" xlink:to="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock_lbl" xml:lang="en-US">Stock options outstanding and exercisable under Company's option plan</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" xlink:label="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" xlink:to="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock_lbl" xml:lang="en-US">Assets under capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" xlink:label="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" xlink:to="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock_lbl" xml:lang="en-US">Future minimum payments required under Capital Leases</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" xlink:label="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" xlink:to="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock_lbl" xml:lang="en-US">Future minimum principal payments related to Long-Term Debt</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SubsequentEventsTablesAbstract" xlink:label="VSTA_SubsequentEventsTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SubsequentEventsTablesAbstract" xlink:to="VSTA_SubsequentEventsTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SubsequentEventsTablesAbstract_lbl" xml:lang="en-US">Subsequent Events Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock" xlink:label="us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock" xlink:to="us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfFutureMinimumRentalPaymentsForOperatingLeasesTableTextBlock_lbl" xml:lang="en-US">Facility lease future minimum payments</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_QuarterlyFinancialInformationTableTextBlock" xlink:label="VSTA_QuarterlyFinancialInformationTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_QuarterlyFinancialInformationTableTextBlock" xlink:to="VSTA_QuarterlyFinancialInformationTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_QuarterlyFinancialInformationTableTextBlock_lbl" xml:lang="en-US">Unaudited Quarterly Results of Operations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_HistoryAndOrganizationDetailsTextualsAbstract" xlink:label="VSTA_HistoryAndOrganizationDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationDetailsTextualsAbstract" xlink:to="VSTA_HistoryAndOrganizationDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_HistoryAndOrganizationDetailsTextualsAbstract_lbl" xml:lang="en-US">Description Of Business Details Textuals</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AwardedByU.S.NationalInstitutes" xlink:label="VSTA_AwardedByU.S.NationalInstitutes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AwardedByU.S.NationalInstitutes" xlink:to="VSTA_AwardedByU.S.NationalInstitutes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AwardedByU.S.NationalInstitutes_lbl" xml:lang="en-US">Awarded by U.S. National Institutes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OutstandingShares" xlink:label="VSTA_OutstandingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShares" xlink:to="VSTA_OutstandingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShares_lbl" xml:lang="en-US">Outstanding shares acquired</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareRepurchase" xlink:label="VSTA_ShareRepurchase" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareRepurchase" xlink:to="VSTA_ShareRepurchase_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareRepurchase_lbl" xml:lang="en-US">Share repurchase</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SharesOutstandingAtMerger" xlink:label="VSTA_SharesOutstandingAtMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesOutstandingAtMerger" xlink:to="VSTA_SharesOutstandingAtMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesOutstandingAtMerger_lbl" xml:lang="en-US">Shares outstanding at merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OutstandingShareRepresentation" xlink:label="VSTA_OutstandingShareRepresentation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShareRepresentation" xlink:to="VSTA_OutstandingShareRepresentation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShareRepresentation_lbl" xml:lang="en-US">Outstanding share representation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NumberOfSharesAuthorizedFollowingAmendment" xlink:label="VSTA_NumberOfSharesAuthorizedFollowingAmendment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfSharesAuthorizedFollowingAmendment" xlink:to="VSTA_NumberOfSharesAuthorizedFollowingAmendment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfSharesAuthorizedFollowingAmendment_lbl" xml:lang="en-US">Number of shares authorized following amendment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" xlink:to="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment_lbl" xml:lang="en-US">Number of Preferred shares authorized following amendment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeriesPreferredStockShares" xlink:label="VSTA_SeriesPreferredStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesPreferredStockShares" xlink:to="VSTA_SeriesPreferredStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredStockShares_lbl" xml:lang="en-US">Series A Preferred Stock shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeriesPreferredShareParValue" xlink:label="VSTA_SeriesPreferredShareParValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesPreferredShareParValue" xlink:to="VSTA_SeriesPreferredShareParValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredShareParValue_lbl" xml:lang="en-US">Series A Preferred share par value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionRateSeriesPreferredShares" xlink:label="VSTA_ConversionRateSeriesPreferredShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionRateSeriesPreferredShares" xlink:to="VSTA_ConversionRateSeriesPreferredShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionRateSeriesPreferredShares_lbl" xml:lang="en-US">Conversion Rate, Series A Preferred shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionTotalSeriesPreferredToCommonStock" xlink:label="VSTA_ConversionTotalSeriesPreferredToCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionTotalSeriesPreferredToCommonStock" xlink:to="VSTA_ConversionTotalSeriesPreferredToCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionTotalSeriesPreferredToCommonStock_lbl" xml:lang="en-US">Conversion total, Series A Preferred to Common</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ConversionToWarrantWarrantValue" xlink:label="VSTA_ConversionToWarrantWarrantValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionToWarrantWarrantValue" xlink:to="VSTA_ConversionToWarrantWarrantValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionToWarrantWarrantValue_lbl" xml:lang="en-US">Conversion to warrant, warrant value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantExercisePrice" xlink:label="VSTA_WarrantExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantExercisePrice" xlink:to="VSTA_WarrantExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantExercisePrice_lbl" xml:lang="en-US">Warrant exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" xlink:label="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" xlink:to="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract_lbl" xml:lang="en-US">Basis Of Presentation And Going Concern Details Textuals</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_2_lbl" xml:lang="en-US">Accumulated Deficit during its development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpectedCashExpenditure" xlink:label="VSTA_ExpectedCashExpenditure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedCashExpenditure" xlink:to="VSTA_ExpectedCashExpenditure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedCashExpenditure_lbl" xml:lang="en-US">Cash expenditure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ProceedsFromIssuancesOfPrivatePlacement" xlink:label="VSTA_ProceedsFromIssuancesOfPrivatePlacement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuancesOfPrivatePlacement" xlink:to="VSTA_ProceedsFromIssuancesOfPrivatePlacement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuancesOfPrivatePlacement_lbl" xml:lang="en-US">Private placement proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xml:lang="en-US">Summary Of Significant Accounting Policies Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xml:lang="en-US">Loss per Common Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xml:lang="en-US">Series A preferred stock issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" xlink:label="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" xlink:to="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement_lbl" xml:lang="en-US">Common stock warants issuable to Platinum upon exchange of Series A preferred stock under the terms of the October 11, 2012 Note Purchase and Exchange Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:to="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_lbl" xml:lang="en-US">Outstanding options under the 2008 and 1999 Stock Incentive Plans</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xml:lang="en-US">Outstanding warrants to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:to="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_lbl" xml:lang="en-US">10% convertible Exchange Note and Investment Notes issued to Platinum in October 2012, February 2013 and March 2013, including accrued interest through March 31, 2013 (2)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Total" xlink:label="VSTA_Total" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Total_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="us-gaap_LiabilitiesFairValueDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="us-gaap_LiabilitiesFairValueDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesFairValueDisclosureAbstract_lbl" xml:lang="en-US">Liabilities, Fair Value Disclosure</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_lbl" xml:lang="en-US">Warrant liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue1" xlink:label="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue1" xlink:to="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue1_lbl" xml:lang="en-US">Put option and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueMeasurementsDetailsTextualsAbstract" xlink:label="VSTA_FairValueMeasurementsDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueMeasurementsDetailsTextualsAbstract" xlink:to="VSTA_FairValueMeasurementsDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueMeasurementsDetailsTextualsAbstract_lbl" xml:lang="en-US">Fair Value Measurements Details Textuals</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ConvertibleNotesPayable" xlink:label="us-gaap_ConvertibleNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayable" xlink:to="us-gaap_ConvertibleNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertibleNotesPayable_lbl" xml:lang="en-US">Convertible promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OriginalPrincipleBalanceOfNotes" xlink:label="VSTA_OriginalPrincipleBalanceOfNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OriginalPrincipleBalanceOfNotes" xlink:to="VSTA_OriginalPrincipleBalanceOfNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OriginalPrincipleBalanceOfNotes_lbl" xml:lang="en-US">Original Principle balance of notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RepaymentOfDebtInPercentage" xlink:label="VSTA_RepaymentOfDebtInPercentage" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RepaymentOfDebtInPercentage" xlink:to="VSTA_RepaymentOfDebtInPercentage_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RepaymentOfDebtInPercentage_lbl" xml:lang="en-US">Repayment of debt in Percentage</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuedWarrantToPurchaseCommonStock" xlink:label="VSTA_IssuedWarrantToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedWarrantToPurchaseCommonStock" xlink:to="VSTA_IssuedWarrantToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuedWarrantToPurchaseCommonStock_lbl" xml:lang="en-US">Issued warrant to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ChangeInFairValueOfTheWarrantLiability" xlink:label="VSTA_ChangeInFairValueOfTheWarrantLiability" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInFairValueOfTheWarrantLiability" xlink:to="VSTA_ChangeInFairValueOfTheWarrantLiability_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInFairValueOfTheWarrantLiability_lbl" xml:lang="en-US">Change in Fair value of the warrant liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" xlink:label="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xml:lang="en-US">Increase in the put option and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" xlink:label="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_lbl" xml:lang="en-US">Remaining put option and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="us-gaap_WarrantsAndRightsOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantsAndRightsOutstanding" xlink:to="us-gaap_WarrantsAndRightsOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WarrantsAndRightsOutstanding_lbl" xml:lang="en-US">Aggregated fair value of the warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_MachineryAndEquipmentGross" xlink:label="us-gaap_MachineryAndEquipmentGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MachineryAndEquipmentGross" xlink:to="us-gaap_MachineryAndEquipmentGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MachineryAndEquipmentGross_lbl" xml:lang="en-US">Laboratory equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ComputersAndNetworkEquipment" xlink:label="VSTA_ComputersAndNetworkEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComputersAndNetworkEquipment" xlink:to="VSTA_ComputersAndNetworkEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComputersAndNetworkEquipment_lbl" xml:lang="en-US">Computers and network equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OfficeFurnitureAndEquipment" xlink:label="VSTA_OfficeFurnitureAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OfficeFurnitureAndEquipment" xlink:to="VSTA_OfficeFurnitureAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OfficeFurnitureAndEquipment_lbl" xml:lang="en-US">Office furniture and equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentGross" xlink:to="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xml:lang="en-US">Property and equipment gross</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xml:lang="en-US">Accumulated depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_Av101AcquisitionDetailsTextualsAbstract" xlink:label="VSTA_Av101AcquisitionDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Av101AcquisitionDetailsTextualsAbstract" xlink:to="VSTA_Av101AcquisitionDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Av101AcquisitionDetailsTextualsAbstract_lbl" xml:lang="en-US">Av-101 Acquisition Details Textuals</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentRate" xlink:label="us-gaap_DebtConversionConvertedInstrumentRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionConvertedInstrumentRate" xlink:to="us-gaap_DebtConversionConvertedInstrumentRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtConversionConvertedInstrumentRate_lbl" xml:lang="en-US">Conversion feature</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeriesB1SharesIssued" xlink:label="VSTA_SeriesB1SharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesB1SharesIssued" xlink:to="VSTA_SeriesB1SharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesB1SharesIssued_lbl" xml:lang="en-US">Series B-1 Shares issued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SeriesB1ValuePerShare" xlink:label="VSTA_SeriesB1ValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesB1ValuePerShare" xlink:to="VSTA_SeriesB1ValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesB1ValuePerShare_lbl" xml:lang="en-US">Series B-1 value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PremergerPurchasePrice" xlink:label="VSTA_PremergerPurchasePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PremergerPurchasePrice" xlink:to="VSTA_PremergerPurchasePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PremergerPurchasePrice_lbl" xml:lang="en-US">Pre-Merger purchase price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AggregateSupportFunding" xlink:label="VSTA_AggregateSupportFunding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateSupportFunding" xlink:to="VSTA_AggregateSupportFunding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateSupportFunding_lbl" xml:lang="en-US">NIH awarded the Company aggregate support</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedExpensesDetailsAbstract" xlink:label="VSTA_AccruedExpensesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesDetailsAbstract" xlink:to="VSTA_AccruedExpensesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedExpensesDetailsAbstract_lbl" xml:lang="en-US">Accrued Expenses Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:label="us-gaap_AccruedProfessionalFeesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedProfessionalFeesCurrent" xlink:to="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xml:lang="en-US">Accrued professional services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedResearchAndDevelopmentExpenses" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedResearchAndDevelopmentExpenses" xlink:to="VSTA_AccruedResearchAndDevelopmentExpenses_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses_lbl" xml:lang="en-US">Accrued research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_AccruedVacationCurrent" xlink:label="us-gaap_AccruedVacationCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedVacationCurrent" xlink:to="us-gaap_AccruedVacationCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedVacationCurrent_lbl" xml:lang="en-US">Accrued vacation pay and other compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedPlacementAgentFees" xlink:label="VSTA_AccruedPlacementAgentFees" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedPlacementAgentFees" xlink:to="VSTA_AccruedPlacementAgentFees_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedPlacementAgentFees_lbl" xml:lang="en-US">Accrued placement agent fees</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AccruedRegistrationRightsPayments" xlink:label="VSTA_AccruedRegistrationRightsPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedRegistrationRightsPayments" xlink:to="VSTA_AccruedRegistrationRightsPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedRegistrationRightsPayments_lbl" xml:lang="en-US">Accrued royalties and license fees</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xml:lang="en-US">All other</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentFaceAmount" xlink:to="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xml:lang="en-US">Principal Balance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestPayableCurrentAndNoncurrent" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPayableCurrentAndNoncurrent" xlink:to="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xml:lang="en-US">Accrued Interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="us-gaap_DebtInstrumentCarryingAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentCarryingAmount" xlink:to="us-gaap_DebtInstrumentCarryingAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentCarryingAmount_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeWarrantAssumptionsAbstract" xlink:label="VSTA_ExchangeWarrantAssumptionsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeWarrantAssumptionsAbstract" xlink:to="VSTA_ExchangeWarrantAssumptionsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeWarrantAssumptionsAbstract_lbl" xml:lang="en-US">Exchange Warrant assumptions:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EquityIssuancePerShareAmount" xlink:label="us-gaap_EquityIssuancePerShareAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityIssuancePerShareAmount" xlink:to="us-gaap_EquityIssuancePerShareAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityIssuancePerShareAmount_lbl" xml:lang="en-US">Market price of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExercisePriceInvestmentWarrants" xlink:label="VSTA_ExercisePriceInvestmentWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePriceInvestmentWarrants" xlink:to="VSTA_ExercisePriceInvestmentWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePriceInvestmentWarrants_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:to="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" xlink:label="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsWeightedAverageVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueInputsPriceEarningsRatioMultiple" xlink:label="us-gaap_FairValueInputsPriceEarningsRatioMultiple" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsPriceEarningsRatioMultiple" xlink:to="us-gaap_FairValueInputsPriceEarningsRatioMultiple_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsPriceEarningsRatioMultiple_lbl" xml:lang="en-US">Fair value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExchangeWarrantNumberOfShares" xlink:label="VSTA_ExchangeWarrantNumberOfShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExchangeWarrantNumberOfShares" xlink:to="VSTA_ExchangeWarrantNumberOfShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExchangeWarrantNumberOfShares_lbl" xml:lang="en-US">Number of shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueAtDateOfIssuance" xlink:label="VSTA_FairValueAtDateOfIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAtDateOfIssuance" xlink:to="VSTA_FairValueAtDateOfIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueAtDateOfIssuance_lbl" xml:lang="en-US">Fair value at date of issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ComponentsOfDiscountAndEffectiveInterestRateForInvestmentNotes" xlink:label="VSTA_ComponentsOfDiscountAndEffectiveInterestRateForInvestmentNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComponentsOfDiscountAndEffectiveInterestRateForInvestmentNotes" xlink:to="VSTA_ComponentsOfDiscountAndEffectiveInterestRateForInvestmentNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComponentsOfDiscountAndEffectiveInterestRateForInvestmentNotes_lbl" xml:lang="en-US">Components of discount and effective interest rate for Investment Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:to="us-gaap_DebtConversionConvertedInstrumentAmount1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1_lbl" xml:lang="en-US">Face value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DiscountAttributableToFairValueOfWarrant" xlink:label="VSTA_DiscountAttributableToFairValueOfWarrant" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountAttributableToFairValueOfWarrant" xlink:to="VSTA_DiscountAttributableToFairValueOfWarrant_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountAttributableToFairValueOfWarrant_lbl" xml:lang="en-US">Discount attributable to fair value of warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_DiscountAttributableToBeneficialConversionFeature" xlink:label="VSTA_DiscountAttributableToBeneficialConversionFeature" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountAttributableToBeneficialConversionFeature" xlink:to="VSTA_DiscountAttributableToBeneficialConversionFeature_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountAttributableToBeneficialConversionFeature_lbl" xml:lang="en-US">Discount attributable to Beneficial conversion feature</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InceptionDateCarryingValue" xlink:label="VSTA_InceptionDateCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InceptionDateCarryingValue" xlink:to="VSTA_InceptionDateCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InceptionDateCarryingValue_lbl" xml:lang="en-US">Inception date carrying value</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentConvertibleEffectiveInterestRate" xlink:label="us-gaap_DebtInstrumentConvertibleEffectiveInterestRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentConvertibleEffectiveInterestRate" xlink:to="us-gaap_DebtInstrumentConvertibleEffectiveInterestRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentConvertibleEffectiveInterestRate_lbl" xml:lang="en-US">Effective Interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_MarketPricePerShare" xlink:label="VSTA_MarketPricePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MarketPricePerShare_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueAssumptionsExercisePrice1" xlink:label="VSTA_FairValueAssumptionsExercisePrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedTerm" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedTerm" xlink:to="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xml:lang="en-US">Expected term (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValuePerShare" xlink:label="VSTA_FairValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValuePerShare_lbl" xml:lang="en-US">Fair Value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentTable_lbl" xml:lang="en-US">Schedule of Long-term Debt Instruments [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xml:lang="en-US">Debt Instrument [Line Items]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" xlink:label="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue" xlink:to="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RegistrationPaymentArrangementAccrualCarryingValue_lbl" xml:lang="en-US">Liability under the Registration Rights Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_July2012PlatinumNoteAmount" xlink:label="VSTA_July2012PlatinumNoteAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_July2012PlatinumNoteAmount" xlink:to="VSTA_July2012PlatinumNoteAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_July2012PlatinumNoteAmount_lbl" xml:lang="en-US">July 2012 Platinum Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_August2012PlatinumNote" xlink:label="VSTA_August2012PlatinumNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_August2012PlatinumNote" xlink:to="VSTA_August2012PlatinumNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_August2012PlatinumNote_lbl" xml:lang="en-US">August 2012 Platinum Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_JulyAndAugustNoteRate" xlink:label="VSTA_JulyAndAugustNoteRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_JulyAndAugustNoteRate" xlink:to="VSTA_JulyAndAugustNoteRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_JulyAndAugustNoteRate_lbl" xml:lang="en-US">July and August note Rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpectedGrossNoteProceeds" xlink:label="VSTA_ExpectedGrossNoteProceeds" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedGrossNoteProceeds" xlink:to="VSTA_ExpectedGrossNoteProceeds_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedGrossNoteProceeds_lbl" xml:lang="en-US">Expected gross note proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_February2012Note" xlink:label="VSTA_February2012Note" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February2012Note" xlink:to="VSTA_February2012Note_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_February2012Note_lbl" xml:lang="en-US">February 2012 Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FebruaryNoteRate" xlink:label="VSTA_FebruaryNoteRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryNoteRate" xlink:to="VSTA_FebruaryNoteRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FebruaryNoteRate_lbl" xml:lang="en-US">February Note rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantValue" xlink:label="VSTA_WarrantValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantValue" xlink:to="VSTA_WarrantValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantValue_lbl" xml:lang="en-US">Warrant value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AggregateShareValue" xlink:label="VSTA_AggregateShareValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateShareValue" xlink:to="VSTA_AggregateShareValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateShareValue_lbl" xml:lang="en-US">Aggregate share value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_RegistrationRightsAgreementLiability" xlink:label="VSTA_RegistrationRightsAgreementLiability" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RegistrationRightsAgreementLiability" xlink:to="VSTA_RegistrationRightsAgreementLiability_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RegistrationRightsAgreementLiability_lbl" xml:lang="en-US">Registration rights agreement liability</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_October2012PlatinumNotePrincipalAmount" xlink:label="VSTA_October2012PlatinumNotePrincipalAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_October2012PlatinumNotePrincipalAmount" xlink:to="VSTA_October2012PlatinumNotePrincipalAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_October2012PlatinumNotePrincipalAmount_lbl" xml:lang="en-US">October 2012 Platinum Note principal amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_October2012PlatinumNoteTranchAmount" xlink:label="VSTA_October2012PlatinumNoteTranchAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_October2012PlatinumNoteTranchAmount" xlink:to="VSTA_October2012PlatinumNoteTranchAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_October2012PlatinumNoteTranchAmount_lbl" xml:lang="en-US">October 2012 Platinum Note tranch amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_October2012PlatinumNoteGrossProceeds" xlink:label="VSTA_October2012PlatinumNoteGrossProceeds" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_October2012PlatinumNoteGrossProceeds" xlink:to="VSTA_October2012PlatinumNoteGrossProceeds_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_October2012PlatinumNoteGrossProceeds_lbl" xml:lang="en-US">October 2012 Platinum Note gross proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PrivatePlacements" xlink:label="VSTA_PrivatePlacements" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrivatePlacements" xlink:to="VSTA_PrivatePlacements_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrivatePlacements_lbl" xml:lang="en-US">Private Placements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PrivatePlacementUnitPrice" xlink:label="VSTA_PrivatePlacementUnitPrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrivatePlacementUnitPrice" xlink:to="VSTA_PrivatePlacementUnitPrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrivatePlacementUnitPrice_lbl" xml:lang="en-US">Private placement unit price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FinancingRequiredToSellNote" xlink:label="VSTA_FinancingRequiredToSellNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FinancingRequiredToSellNote" xlink:to="VSTA_FinancingRequiredToSellNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FinancingRequiredToSellNote_lbl" xml:lang="en-US">Financing required to sell Note</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LegalEntityAxis" xlink:to="dei_LegalEntityAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="dei_LegalEntityAxis_2_lbl" xml:lang="en-US">Legal Entity [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_UnsecuredLongTermDebt" xlink:label="us-gaap_UnsecuredLongTermDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnsecuredLongTermDebt" xlink:to="us-gaap_UnsecuredLongTermDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnsecuredLongTermDebt_lbl" xml:lang="en-US">New unsecured promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xml:lang="en-US">Shares Exercisable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xml:lang="en-US">Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_AwardTypeAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AwardTypeAxis_2_lbl" xml:lang="en-US">Award Type [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xml:lang="en-US">Assumption:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExercisePricePerShareWeightedAvg" xlink:label="VSTA_ExercisePricePerShareWeightedAvg" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePricePerShareWeightedAvg" xlink:to="VSTA_ExercisePricePerShareWeightedAvg_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePricePerShareWeightedAvg_lbl" xml:lang="en-US">Exercise price per share (weighted average)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_lbl" xml:lang="en-US">Exercise price per share Upper</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_lbl" xml:lang="en-US">Risk-free interest rate Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_lbl" xml:lang="en-US">Risk-free interest rate Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xml:lang="en-US">Expected term (years) Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpectedTermYearsMaximum" xlink:label="VSTA_ExpectedTermYearsMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedTermYearsMaximum" xlink:to="VSTA_ExpectedTermYearsMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedTermYearsMaximum_lbl" xml:lang="en-US">Expected term (years) Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_lbl" xml:lang="en-US">Volatility Minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_lbl" xml:lang="en-US">Volatility Maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WeightedAverageFairValuePerShare" xlink:label="VSTA_WeightedAverageFairValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageFairValuePerShare" xlink:to="VSTA_WeightedAverageFairValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageFairValuePerShare_lbl" xml:lang="en-US">Weighted Average Fair Value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantsOptionAbstract" xlink:label="VSTA_WarrantsOptionAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsOptionAbstract" xlink:to="VSTA_WarrantsOptionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsOptionAbstract_lbl" xml:lang="en-US">Warrants option</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExercisePrice" xlink:label="VSTA_ExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePrice" xlink:to="VSTA_ExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePrice_lbl" xml:lang="en-US">Exercise Price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpirationDate" xlink:label="VSTA_ExpirationDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpirationDate" xlink:to="VSTA_ExpirationDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpirationDate_lbl" xml:lang="en-US">Expiration Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_lbl" xml:lang="en-US">Number of Warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CapitalStockDetails2Abstract" xlink:label="VSTA_CapitalStockDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockDetails2Abstract" xlink:to="VSTA_CapitalStockDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockDetails2Abstract_lbl" xml:lang="en-US">Capital Stock Details 2</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:to="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xml:lang="en-US">Upon exchange of all shares of Series A Preferred Stock currently issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" xlink:label="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" xlink:to="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement_lbl" xml:lang="en-US">Warrant shares issuable to Platinum upon exercise of common stock warrant upon exchange of Series A preferred stock under the terms of the October 11, 2012 Note Purchase and Exchange Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" xlink:label="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" xlink:to="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2_lbl" xml:lang="en-US">110% of shares issuable upon conversion of 10% convertible Exchange Note and Investment Notes issued to Platinum in October 2012, February 2013 and March 2013, including interest accrued through maturity (2)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PursuantToWarrantsToPurchaseCommonStock" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToWarrantsToPurchaseCommonStock" xlink:to="VSTA_PursuantToWarrantsToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStock_lbl" xml:lang="en-US">Pursuant to warrants to purchase common stock:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xml:lang="en-US">Subject to outstanding warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" xlink:label="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" xlink:to="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork_lbl" xml:lang="en-US">Issuable pursuant to accrued interest through maturity on outstanding promissory notes issued to Morrison &amp; Foerster, Cato Research Ltd., and University Health Network</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" xlink:to="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal_lbl" xml:lang="en-US">Pursuant to warrants to purchase common stock, total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PursuantToStockIncentivePlans" xlink:label="VSTA_PursuantToStockIncentivePlans" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToStockIncentivePlans" xlink:to="VSTA_PursuantToStockIncentivePlans_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToStockIncentivePlans_lbl" xml:lang="en-US">Pursuant to stock incentive plans:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" xlink:label="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" xlink:to="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans_lbl" xml:lang="en-US">Subject to outstanding options under the 2008 and 1999 Stock Incentive Plans</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xml:lang="en-US">Available for future grants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" xlink:label="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" xlink:to="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares_lbl" xml:lang="en-US">Pursuant to stock incentive plans, total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" xlink:label="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" xlink:to="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits_lbl" xml:lang="en-US">Upon sales of additional Units pursuant to the 2012 Private Placement of Units</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xml:lang="en-US">Total</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementClassOfStockAxis" xlink:to="us-gaap_StatementClassOfStockAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StatementClassOfStockAxis_2_lbl" xml:lang="en-US">Class of Stock [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesPurchasedForAward_lbl" xml:lang="en-US">Purchase of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2012/invest-2012-01-31.xsd#invest_InvestmentOptionsExercisePrice" xlink:label="invest_InvestmentOptionsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="invest_InvestmentOptionsExercisePrice" xlink:to="invest_InvestmentOptionsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="invest_InvestmentOptionsExercisePrice_lbl" xml:lang="en-US">Common stock, exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:to="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xml:lang="en-US">Fair value of warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SharePrice1" xlink:label="VSTA_SharePrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePrice1" xlink:to="VSTA_SharePrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_SharePrice1_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_lbl" xml:lang="en-US">Common stock exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ContractualTerm1" xlink:label="VSTA_ContractualTerm1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ContractualTerm1" xlink:to="VSTA_ContractualTerm1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ContractualTerm1_lbl" xml:lang="en-US">Contractual term</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_FairValueAssumptionsExpectedDividendRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate_2_lbl" xml:lang="en-US">Expected dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_lbl" xml:lang="en-US">Common stock granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockValue1" xlink:label="VSTA_CommonStockValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockValue1" xlink:to="VSTA_CommonStockValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockValue1_lbl" xml:lang="en-US">Common stock granted value</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePrice1" xlink:to="VSTA_SharePrice1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharePrice1_2_lbl" xml:lang="en-US">Common stock granted date market price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xml:lang="en-US">Cash proceeds from common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmountsDueForServices" xlink:label="VSTA_AmountsDueForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountsDueForServices" xlink:to="VSTA_AmountsDueForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmountsDueForServices_lbl" xml:lang="en-US">Amounts due for services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockPurchseDiscription" xlink:label="VSTA_CommonStockPurchseDiscription" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockPurchseDiscription" xlink:to="VSTA_CommonStockPurchseDiscription_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockPurchseDiscription_lbl" xml:lang="en-US">Common stock purchse discription</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncreasedValueOfWarrantsExercised" xlink:label="VSTA_IncreasedValueOfWarrantsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreasedValueOfWarrantsExercised" xlink:to="VSTA_IncreasedValueOfWarrantsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncreasedValueOfWarrantsExercised_lbl" xml:lang="en-US">Increased value of warrants exercised</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_2_lbl" xml:lang="en-US">common stock at a weighted average exercise price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PreferredStockSharesIssued_2_lbl" xml:lang="en-US">Preferred stock issued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommonStockOwned" xlink:label="VSTA_CommonStockOwned" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockOwned" xlink:to="VSTA_CommonStockOwned_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockOwned_lbl" xml:lang="en-US">Common stock owned</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SecuredConvertiblePromissoryNote1" xlink:label="VSTA_SecuredConvertiblePromissoryNote1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SecuredConvertiblePromissoryNote1" xlink:to="VSTA_SecuredConvertiblePromissoryNote1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SecuredConvertiblePromissoryNote1_lbl" xml:lang="en-US">Secured convertible promissory note</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayable" xlink:to="us-gaap_ConvertibleNotesPayable_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ConvertibleNotesPayable_2_lbl" xml:lang="en-US">Convertible promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FinancingTransactionsGrossProceeds" xlink:label="VSTA_FinancingTransactionsGrossProceeds" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FinancingTransactionsGrossProceeds" xlink:to="VSTA_FinancingTransactionsGrossProceeds_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FinancingTransactionsGrossProceeds_lbl" xml:lang="en-US">Financing transactions gross proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_InvestmentInQualifiedFinancing" xlink:label="VSTA_InvestmentInQualifiedFinancing" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentInQualifiedFinancing" xlink:to="VSTA_InvestmentInQualifiedFinancing_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InvestmentInQualifiedFinancing_lbl" xml:lang="en-US">Investment in Qualified Financing</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:to="VSTA_AmountOfCommitmentsFromOtherInvestors_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors_lbl" xml:lang="en-US">Amount of commitments from other investors</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:to="VSTA_PeriodOfCommitmentsFromOtherInvestors2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2_lbl" xml:lang="en-US">Period of commitments from other investors</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_2_lbl" xml:lang="en-US">Securities stated value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xml:lang="en-US">Authorized and outstanding shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpense_2_lbl" xml:lang="en-US">Research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncomeTaxesDetailsAbstract" xlink:label="VSTA_IncomeTaxesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncomeTaxesDetailsAbstract" xlink:to="VSTA_IncomeTaxesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncomeTaxesDetailsAbstract_lbl" xml:lang="en-US">Income Taxes Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xml:lang="en-US">Computed expected tax benefit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_LossesNotBenefitted" xlink:label="VSTA_LossesNotBenefitted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossesNotBenefitted" xlink:to="VSTA_LossesNotBenefitted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossesNotBenefitted_lbl" xml:lang="en-US">Losses not benefitted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_EffectiveIncomeTaxRateReconciliationOther" xlink:label="VSTA_EffectiveIncomeTaxRateReconciliationOther" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectiveIncomeTaxRateReconciliationOther" xlink:to="VSTA_EffectiveIncomeTaxRateReconciliationOther_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_EffectiveIncomeTaxRateReconciliationOther_lbl" xml:lang="en-US">Other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xml:lang="en-US">Income tax expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_IncomeTaxesDetails1Abstract" xlink:label="VSTA_IncomeTaxesDetails1Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncomeTaxesDetails1Abstract" xlink:to="VSTA_IncomeTaxesDetails1Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncomeTaxesDetails1Abstract_lbl" xml:lang="en-US">Income Taxes Details 1</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xml:lang="en-US">Net operating loss carry-forwards</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_BasisDifferencesInFixedAssets" xlink:label="VSTA_BasisDifferencesInFixedAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BasisDifferencesInFixedAssets" xlink:to="VSTA_BasisDifferencesInFixedAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BasisDifferencesInFixedAssets_lbl" xml:lang="en-US">Basis differences in fixed assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals_lbl" xml:lang="en-US">Accruals and reserves</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsGross" xlink:label="us-gaap_DeferredTaxAssetsGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsGross" xlink:to="us-gaap_DeferredTaxAssetsGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xml:lang="en-US">Total deferred tax assets, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsValuationAllowance" xlink:to="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xml:lang="en-US">Valuation allowance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="us-gaap_DeferredTaxAssetsNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsNet" xlink:to="us-gaap_DeferredTaxAssetsNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xml:lang="en-US">Net deferred tax asset</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" xlink:label="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" xlink:to="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease_lbl" xml:lang="en-US">Valuation allowance increase</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xml:lang="en-US">U.S. federal net operating loss carryforwards</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xml:lang="en-US">state net operating loss carryforwards</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpectedDividendYield" xlink:label="VSTA_ExpectedDividendYield" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedDividendYield" xlink:to="VSTA_ExpectedDividendYield_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedDividendYield_lbl" xml:lang="en-US">Expected dividend yield</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:to="us-gaap_TemporaryEquityRedemptionPricePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharePrice_lbl" xml:lang="en-US">Market price on date of grant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValueAssumptionsRiskFreeInterestRates" xlink:label="VSTA_FairValueAssumptionsRiskFreeInterestRates" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsRiskFreeInterestRates" xlink:to="VSTA_FairValueAssumptionsRiskFreeInterestRates_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_FairValueAssumptionsRiskFreeInterestRates_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ExpectedYearTerm" xlink:label="VSTA_ExpectedYearTerm" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedYearTerm" xlink:to="VSTA_ExpectedYearTerm_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedYearTerm_lbl" xml:lang="en-US">Expected (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FairValuePerShareAtGrantDate" xlink:label="VSTA_FairValuePerShareAtGrantDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShareAtGrantDate" xlink:to="VSTA_FairValuePerShareAtGrantDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValuePerShareAtGrantDate_lbl" xml:lang="en-US">Fair value per share at grant date</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_NumberOfShares" xlink:label="VSTA_NumberOfShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfShares" xlink:to="VSTA_NumberOfShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfShares_lbl" xml:lang="en-US">Number of Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xml:lang="en-US">Options outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xml:lang="en-US">Options granted</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod_lbl" xml:lang="en-US">Options exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2_lbl" xml:lang="en-US">Options cancelled</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xml:lang="en-US">Options forfeited</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_lbl" xml:lang="en-US">Options expired</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xml:lang="en-US">Options outstanding at end of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_2_lbl" xml:lang="en-US">Options exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_WeightedAverageExercisePrice" xlink:label="VSTA_WeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageExercisePrice" xlink:to="VSTA_WeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted Average Exercise Price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2_lbl" xml:lang="en-US">Options exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options cancelled</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options forfeited</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options expired</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xml:lang="en-US">Options outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xml:lang="en-US">Weighted average grant-date fair value of options granted during the period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestIncomeExpenseNet" xlink:to="us-gaap_InterestIncomeExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xml:lang="en-US">Total interest expense on note and the prior line of credit</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xml:lang="en-US">Incurred expenses on research and subsequent other projects</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CrlNoteIntrestExpense" xlink:label="VSTA_CrlNoteIntrestExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CrlNoteIntrestExpense" xlink:to="VSTA_CrlNoteIntrestExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CrlNoteIntrestExpense_lbl" xml:lang="en-US">CRL note interest expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeaseObligationsAbstract" xlink:label="us-gaap_CapitalLeaseObligationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsAbstract" xlink:to="us-gaap_CapitalLeaseObligationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsAbstract_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" xlink:to="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment_lbl" xml:lang="en-US">Leased laboratory and computer equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" xlink:to="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation_lbl" xml:lang="en-US">Accumulated amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_LeasedLaboratoryAndComputerEquipmentNet" xlink:label="VSTA_LeasedLaboratoryAndComputerEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LeasedLaboratoryAndComputerEquipmentNet" xlink:to="VSTA_LeasedLaboratoryAndComputerEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LeasedLaboratoryAndComputerEquipmentNet_lbl" xml:lang="en-US">Leased laboratory and computer equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details 1</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract_lbl" xml:lang="en-US">Future minimum payment, capital leases, Equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent_lbl" xml:lang="en-US">Lease payment 2014</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xml:lang="en-US">Lease payment 2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xml:lang="en-US">Lease payment 2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears_lbl" xml:lang="en-US">Lease payment 2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xml:lang="en-US">Lease payment 2018</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDue" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDue" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDue_lbl" xml:lang="en-US">Future minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments_lbl" xml:lang="en-US">Less imputed interest included in minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments_lbl" xml:lang="en-US">Present value of minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CapitalLeaseObligationsEquipmentCurrent" xlink:label="VSTA_CapitalLeaseObligationsEquipmentCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalLeaseObligationsEquipmentCurrent" xlink:to="VSTA_CapitalLeaseObligationsEquipmentCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalLeaseObligationsEquipmentCurrent_lbl" xml:lang="en-US">Less current portion</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsNoncurrent" xlink:to="us-gaap_CapitalLeaseObligationsNoncurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent_2_lbl" xml:lang="en-US">Non-current capital lease obligation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details 2</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FutureMinimumPaymentsPrincipal" xlink:label="VSTA_FutureMinimumPaymentsPrincipal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FutureMinimumPaymentsPrincipal" xlink:to="VSTA_FutureMinimumPaymentsPrincipal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FutureMinimumPaymentsPrincipal_lbl" xml:lang="en-US">Future minimum payments, principal</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_lbl" xml:lang="en-US">2014</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_lbl" xml:lang="en-US">2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_lbl" xml:lang="en-US">2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_lbl" xml:lang="en-US">2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_lbl" xml:lang="en-US">2018</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_lbl" xml:lang="en-US">Thereafter through October 2023</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FutureMinimumPrincipalPayments" xlink:label="VSTA_FutureMinimumPrincipalPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FutureMinimumPrincipalPayments" xlink:to="VSTA_FutureMinimumPrincipalPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_FutureMinimumPrincipalPayments_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesRentExpenseMinimumRentals" xlink:label="us-gaap_OperatingLeasesRentExpenseMinimumRentals" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesRentExpenseMinimumRentals" xlink:to="us-gaap_OperatingLeasesRentExpenseMinimumRentals_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesRentExpenseMinimumRentals_lbl" xml:lang="en-US">Future minimum payments under operating leases</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesRentExpenseNet" xlink:label="us-gaap_OperatingLeasesRentExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesRentExpenseNet" xlink:to="us-gaap_OperatingLeasesRentExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesRentExpenseNet_lbl" xml:lang="en-US">Facility rent expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SubsequentEventsDetailsAbstract" xlink:label="VSTA_SubsequentEventsDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SubsequentEventsDetailsAbstract" xlink:to="VSTA_SubsequentEventsDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SubsequentEventsDetailsAbstract_lbl" xml:lang="en-US">Subsequent Events Details</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_FutureMinimumPaymentOperatingLease" xlink:label="VSTA_FutureMinimumPaymentOperatingLease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FutureMinimumPaymentOperatingLease" xlink:to="VSTA_FutureMinimumPaymentOperatingLease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FutureMinimumPaymentOperatingLease_lbl" xml:lang="en-US">Future minimum payment, operating lease</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent_lbl" xml:lang="en-US">Lease payment 2014</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xml:lang="en-US">Lease payment 2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xml:lang="en-US">Lease payment 2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xml:lang="en-US">Lease payment 2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xml:lang="en-US">Lease payment 2018</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" xlink:label="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" xlink:to="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding_lbl" xml:lang="en-US">Shares of common stock retroactively reflected as outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2012/elts/us-gaap-2012-01-31.xsd#us-gaap_UnitsOfPartnershipInterestAmount" xlink:label="us-gaap_UnitsOfPartnershipInterestAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnitsOfPartnershipInterestAmount" xlink:to="us-gaap_UnitsOfPartnershipInterestAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnitsOfPartnershipInterestAmount_lbl" xml:lang="en-US">Shares held by stockholders, pre-merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20130331.xsd#VSTA_SupplementalFinancialInformationDetails2Abstract" xlink:label="VSTA_SupplementalFinancialInformationDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SupplementalFinancialInformationDetails2Abstract" xlink:to="VSTA_SupplementalFinancialInformationDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SupplementalFinancialInformationDetails2Abstract_lbl" xml:lang="en-US">Supplemental Financial Information Details</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Revenues_2_lbl" xml:lang="en-US">Total revenues</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpenses_2_lbl" xml:lang="en-US">Total operating expenses</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingIncomeLoss_2_lbl" xml:lang="en-US">Loss from operations</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxExpenseBenefit_2_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_NetIncomeLoss_3_lbl" xml:lang="en-US">Net loss</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeferredRevenues" xlink:to="VSTA_DeferredRevenues_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DeferredRevenues_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion" xlink:to="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertiblePromissoryNotesNetOfCurrentPortion_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedOfficersCompensation" xlink:to="VSTA_AccruedOfficersCompensation_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedOfficersCompensation_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RevenueFromExternalCustomers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AcquiredInProcessResearchAndDevelopment" xlink:to="VSTA_AcquiredInProcessResearchAndDevelopment_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AcquiredInProcessResearchAndDevelopment_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComprehensiveLoss" xlink:to="VSTA_ComprehensiveLoss_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ComprehensiveLoss_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOn77.5And10Notes" xlink:to="VSTA_AmortizationOfDiscountsOn77.5And10Notes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOn77.5And10Notes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnPlatinumNotes" xlink:to="VSTA_AmortizationOfDiscountsOnPlatinumNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnPlatinumNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes" xlink:to="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnAugust2010ShortTermNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes" xlink:to="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfDiscountsOnFebruary201212ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes" xlink:to="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmortizationOfImputedDiscountOnNonInterestBearingNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:to="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf20082010NotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotesPayable" xlink:to="VSTA_ProceedsFromIssuanceOf7NotesPayable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromIssuanceOf7NotesPayable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfAugust2010ShortTermNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_HistoryAndOrganizationTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesTextBlock" xlink:to="VSTA_AccruedExpensesTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedExpensesTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LicensingAndCollaborativeAgreementsTextBlock" xlink:to="VSTA_LicensingAndCollaborativeAgreementsTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LicensingAndCollaborativeAgreementsTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockTextBlock" xlink:to="VSTA_CapitalStockTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CapitalStockTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesPerValue1_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesIssued_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan" xlink:to="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingOptionsUnder2008And1999StockIncentivePlanAnd1998ScientificAdvisoryBoardPlan_doc" xml:lang="en-US">Outstanding Options Under 2008 And 1999 Stock Incentive Plan And 1998 Scientific Advisory Board Plan.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xml:lang="en-US">Outstanding Warrants To Purchase Common Stock.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1" xlink:to="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_February201212ConvertiblePromissoryNotesAndAccruedInterest1_doc" xml:lang="en-US">February 2012 12 Convertible Promissory Notes And Accrued Interest1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_Total_doc" xml:lang="en-US">Total.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedResearchAndDevelopmentExpenses" xlink:to="VSTA_AccruedResearchAndDevelopmentExpenses_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedResearchAndDevelopmentExpenses_doc" xml:lang="en-US">Accrued Research And Development Expenses.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedPlacementAgentFees" xlink:to="VSTA_AccruedPlacementAgentFees_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedPlacementAgentFees_doc" xml:lang="en-US">Accrued Placement Agent Fees.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedRegistrationRightsPayments" xlink:to="VSTA_AccruedRegistrationRightsPayments_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedRegistrationRightsPayments_doc" xml:lang="en-US">Accrued Registration Rights Payments.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationWarrantsMember" xlink:to="VSTA_PreModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationWarrantsMember_doc" xml:lang="en-US">Pre Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationWarrantsMember" xlink:to="VSTA_PostModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationWarrantsMember_doc" xml:lang="en-US">Post Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MarketPricePerShare_doc" xml:lang="en-US">Market Price Per Share.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedTermYearsMaximum" xlink:to="VSTA_ExpectedTermYearsMaximum_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpectedTermYearsMaximum_doc" xml:lang="en-US">Expected Term Years Maximum.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageFairValuePerShare" xlink:to="VSTA_WeightedAverageFairValuePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WeightedAverageFairValuePerShare_doc" xml:lang="en-US">Weighted Average Fair Value Per Share.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsOneMember" xlink:to="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xml:lang="en-US">Share Based Compensation Warrants One Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwoMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xml:lang="en-US">Share Based Compensation Warrants Two Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFourMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xml:lang="en-US">Share Based Compensation Warrants Four Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFiveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Five Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSixMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xml:lang="en-US">Share Based Compensation Warrants Six Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Seven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsEightMember" xlink:to="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eight Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsNineMember" xlink:to="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xml:lang="en-US">Share Based Compensation Warrants Nine Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Ten Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsElevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eleven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwelveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Twelve Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePrice" xlink:to="VSTA_ExercisePrice_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExercisePrice_doc" xml:lang="en-US">Exercise Price.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" xlink:to="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_doc" xml:lang="en-US">Convertible Promissory Notes And Other Notes Payable Table Text Block.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock_doc" xml:lang="en-US">Blackscholes Option Pricing Model Table Text Block.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AwardedByU.S.NationalInstitutes" xlink:to="VSTA_AwardedByU.S.NationalInstitutes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AwardedByU.S.NationalInstitutes_doc" xml:lang="en-US">Awarded By U.S. National Institutes.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShares" xlink:to="VSTA_OutstandingShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingShares_doc" xml:lang="en-US">Outstanding Shares.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OriginalPrincipleBalanceOfNotes" xlink:to="VSTA_OriginalPrincipleBalanceOfNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OriginalPrincipleBalanceOfNotes_doc" xml:lang="en-US">Original Principle Balance Of Notes.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RepaymentOfDebtInPercentage" xlink:to="VSTA_RepaymentOfDebtInPercentage_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RepaymentOfDebtInPercentage_doc" xml:lang="en-US">Repayment Of Debt In Percentage.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedWarrantToPurchaseCommonStock" xlink:to="VSTA_IssuedWarrantToPurchaseCommonStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuedWarrantToPurchaseCommonStock_doc" xml:lang="en-US">Issued Warrant To Purchase Common Stock.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInFairValueOfTheWarrantLiability" xlink:to="VSTA_ChangeInFairValueOfTheWarrantLiability_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInFairValueOfTheWarrantLiability_doc" xml:lang="en-US">Change In Fair Value Of The Warrant Liability.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncreaseInPutOptionAndNoteTermExtensionOptionLiabilities_doc" xml:lang="en-US">Increase In Put Option And Note Term Extension Option Liabilities.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities" xlink:to="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RemainingPutOptionAndNoteTermExtensionOptionLiabilities_doc" xml:lang="en-US">Remaining Put Option And Note Term Extension Option Liabilities.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February2012ConvertibleNotes12PercentMember" xlink:to="VSTA_February2012ConvertibleNotes12PercentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_February2012ConvertibleNotes12PercentMember_doc" xml:lang="en-US">February 2012 Convertible Notes 12 Percent Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsMember" xlink:to="VSTA_DesjardinsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DesjardinsMember_doc" xml:lang="en-US">Desjardins Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationServicesMember" xlink:to="VSTA_InvestorRelationServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestorRelationServicesMember_doc" xml:lang="en-US">Investor Relation Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationsAndPublicCompanyServicesMember" xlink:to="VSTA_InvestorRelationsAndPublicCompanyServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestorRelationsAndPublicCompanyServicesMember_doc" xml:lang="en-US">Investor Relations And Public Company Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AdditionalInvestorRelationsServicesMember" xlink:to="VSTA_AdditionalInvestorRelationsServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AdditionalInvestorRelationsServicesMember_doc" xml:lang="en-US">Additional Investor Relations Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantModificationsMember" xlink:to="VSTA_WarrantModificationsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WarrantModificationsMember_doc" xml:lang="en-US">Warrant Modifications Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForegoingExercisesMember" xlink:to="VSTA_ForegoingExercisesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForegoingExercisesMember_doc" xml:lang="en-US">Foregoing Exercises Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumMember" xlink:to="VSTA_PlatinumMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PlatinumMember_doc" xml:lang="en-US">Platinum Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_QualifiedFinancingMember" xlink:to="VSTA_QualifiedFinancingMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_QualifiedFinancingMember_doc" xml:lang="en-US">Qualified Financing Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePrice1" xlink:to="VSTA_SharePrice1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SharePrice1_doc" xml:lang="en-US">Share Price1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardPerShareWeightedAveragePriceOfSharesPurchased1_doc" xml:lang="en-US">Share Based Compensation Arrangement By Share Based Payment Award Per Share Weighted Average Price Of Shares Purchased1</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant1_doc" xml:lang="en-US">Share Based Compensation Arrangement By ShareBased Payment Award Number Of Shares Available For Grant1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockValue1" xlink:to="VSTA_CommonStockValue1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockValue1_doc" xml:lang="en-US">Common Stock Value1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountsDueForServices" xlink:to="VSTA_AmountsDueForServices_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmountsDueForServices_doc" xml:lang="en-US">Amounts Due For Services.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockPurchseDiscription" xlink:to="VSTA_CommonStockPurchseDiscription_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockPurchseDiscription_doc" xml:lang="en-US">Common Stock Purchse Discription.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncreasedValueOfWarrantsExercised" xlink:to="VSTA_IncreasedValueOfWarrantsExercised_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncreasedValueOfWarrantsExercised_doc" xml:lang="en-US">Increased Value Of Warrants Exercised.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockOwned" xlink:to="VSTA_CommonStockOwned_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockOwned_doc" xml:lang="en-US">Common Stock Owned.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SecuredConvertiblePromissoryNote1" xlink:to="VSTA_SecuredConvertiblePromissoryNote1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SecuredConvertiblePromissoryNote1_doc" xml:lang="en-US">Secured Convertible Promissory Note1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FinancingTransactionsGrossProceeds" xlink:to="VSTA_FinancingTransactionsGrossProceeds_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FinancingTransactionsGrossProceeds_doc" xml:lang="en-US">Financing Transactions Gross Proceeds.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestmentInQualifiedFinancing" xlink:to="VSTA_InvestmentInQualifiedFinancing_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestmentInQualifiedFinancing_doc" xml:lang="en-US">Investment In Qualified Financing.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AmountOfCommitmentsFromOtherInvestors" xlink:to="VSTA_AmountOfCommitmentsFromOtherInvestors_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AmountOfCommitmentsFromOtherInvestors_doc" xml:lang="en-US">Amount Of Commitments From Other Investors.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoHoldingCompanyMember" xlink:to="VSTA_CatoHoldingCompanyMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoHoldingCompanyMember_doc" xml:lang="en-US">Cato Holding Company Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ContractualTerm1" xlink:to="VSTA_ContractualTerm1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ContractualTerm1_doc" xml:lang="en-US">Contractual Term1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PeriodOfCommitmentsFromOtherInvestors2" xlink:to="VSTA_PeriodOfCommitmentsFromOtherInvestors2_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PeriodOfCommitmentsFromOtherInvestors2_doc" xml:lang="en-US">Period Of Commitments From Other Investors2</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpirationDate" xlink:to="VSTA_ExpirationDate_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpirationDate_doc" xml:lang="en-US">Expiration Date.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscount_doc" xml:lang="en-US">Notes Payable Discount.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscountRelatedParties_doc" xml:lang="en-US">Notes Payable Discount Related Parties.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNotesDiscount" xlink:to="VSTA_ConvertibleNotesDiscount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConvertibleNotesDiscount_doc" xml:lang="en-US">Convertible Notes Discount.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePricePerShareWeightedAvg" xlink:to="VSTA_ExercisePricePerShareWeightedAvg_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExercisePricePerShareWeightedAvg_doc" xml:lang="en-US">Exercise Price Per Share Weighted Avg.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationMember" xlink:to="VSTA_PreModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationMember" xlink:to="VSTA_PostModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValuePerShare_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoBioVenturesMember" xlink:to="VSTA_CatoBioVenturesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoBioVenturesMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_USNationalInstitutesOfHealthMember" xlink:to="VSTA_USNationalInstitutesOfHealthMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_USNationalInstitutesOfHealthMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NIHGrantRevenueMember" xlink:to="VSTA_NIHGrantRevenueMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NIHGrantRevenueMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoResearchLtdMember" xlink:to="VSTA_CatoResearchLtdMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoResearchLtdMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfAmendedMfWarrant" xlink:to="VSTA_IncrementalValueOfAmendedMfWarrant_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfAmendedMfWarrant_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuedToPlatinumOnTwoJulyTwoThousandTwelveMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember" xlink:to="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuedToPlatinumOnThirtyAugustTwoThousandTwelveMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNotesNonCurrentMember" xlink:to="VSTA_SeniorNotesNonCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeniorNotesNonCurrentMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountMember" xlink:to="VSTA_NoteDiscountMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember" xlink:to="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableAugustTwoThousandTwelveMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableMember" xlink:to="VSTA_SevenPercentNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionMember" xlink:to="VSTA_CurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableNonCurrentPortionMember" xlink:to="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableNonCurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BurrPilgerMayerMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_McCarthyTetraultMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteAMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember" xlink:to="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AugustTwoThousandTwelveMorrisonAndFoersterNoteBMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountOneMember" xlink:to="VSTA_NoteDiscountOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPointFivePercentNotesPayableMember" xlink:to="VSTA_SevenPointFivePercentNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPointFivePercentNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionOneMember" xlink:to="VSTA_CurrentPortionOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountMember" xlink:to="VSTA_NonCurrentPortionAndDiscountMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember" xlink:to="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FivePointEightPercentAndEightPercentNotesPayableToInsurancePremiumFinancingCompanyCurrentMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember" xlink:to="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TenPercentNotesPayableToVendorsForAccountsPayableConvertedToNotesPayableMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionTwoMember" xlink:to="VSTA_CurrentPortionTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionMember" xlink:to="VSTA_NonCurrentPortionMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember" xlink:to="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TenPercentNotesPayableToUnrelatedPartiesMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionThreeMember" xlink:to="VSTA_CurrentPortionThreeMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionThreeMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountOneMember" xlink:to="VSTA_NonCurrentPortionAndDiscountOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountOneMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotePayableToCatoHoldingMember" xlink:to="VSTA_SevenPercentNotePayableToCatoHoldingMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotePayableToCatoHoldingMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountTwoMember" xlink:to="VSTA_NoteDiscountTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableToRelatedPartiesMember" xlink:to="VSTA_NotesPayableToRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionFourMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NonCurrentPortionAndDiscountTwoMember" xlink:to="VSTA_NonCurrentPortionAndDiscountTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NonCurrentPortionAndDiscountTwoMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember" xlink:to="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FebruaryTwoThousandTwelveTwelvePercentConvertiblePromissoryNotesMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember" xlink:to="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_TwelvePercentConvertibleNotesNetNnonCurrentMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsMember" xlink:to="VSTA_ShareBasedCompensationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesB1PreferredStockMember" xlink:to="VSTA_SeriesB1PreferredStockMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeriesB1PreferredStockMember_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockholdersEquityForPreferredStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SharesIssuedForPreferredStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf5500Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount" xlink:to="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares" xlink:to="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesbPreferredStockat5.545PerShareForCashNetOfissuanceCostsOf97200Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockat6.00PerShareForCashNetOfissuanceCostsOf20700Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfStockMember" xlink:to="VSTA_NotesReceivableFromSaleOfStockMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesReceivableFromSaleOfStockMember_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember" xlink:to="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DeficitAccumulatedDuringTheDevelopmentStageMember_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InitialSaleOfCommonStockForCashToFounderAmount" xlink:to="VSTA_InitialSaleOfCommonStockForCashToFounderAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InitialSaleOfCommonStockForCashToFounderShares" xlink:to="VSTA_InitialSaleOfCommonStockForCashToFounderShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InitialSaleOfCommonStockForCashToFounderShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForServicesAmount" xlink:to="VSTA_FairValueOfCommonStockIssuedForServicesAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForServicesShares" xlink:to="VSTA_FairValueOfCommonStockIssuedForServicesShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockIssuedForServicesShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerAmount" xlink:to="VSTA_EffectOfMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerShares" xlink:to="VSTA_EffectOfMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashAmount" xlink:to="VSTA_SaleOfCommonStockForCashAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SaleOfCommonStockForCashAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashShares" xlink:to="VSTA_SaleOfCommonStockForCashShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SaleOfCommonStockForCashShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServices" xlink:to="VSTA_FairValueOfWarrantsIssuedForServices_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith7ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWith10ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriescPreferredStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForCashShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForDebtCancellationShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAndWarrantsForNotesReceivableShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharebasedCompensationExpense" xlink:to="VSTA_SharebasedCompensationExpense_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SharebasedCompensationExpense_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount" xlink:to="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares" xlink:to="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponSettlementOfEmploymentContractShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnNotesReceivable" xlink:to="VSTA_AccruedInterestOnNotesReceivable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedInterestOnNotesReceivable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom2008StockIncentivePlanAndScientificAdvisoryPlanShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfReverseStockSplit" xlink:to="VSTA_EffectOfReverseStockSplit_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfReverseStockSplit_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:to="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfWarrantShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfWarrantShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfWarrantShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_doc" xlink:type="arc" />
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForServicesAmount" xlink:to="VSTA_CommonStockIssuedForServicesAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedForServicesAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForServicesShares" xlink:to="VSTA_CommonStockIssuedForServicesShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedForServicesShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_FairValueOfWarrantsIssuedForServicesAndIncrementalFairValueOfWarrantModification_doc" xlink:type="arc" />
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWith7.5Notes_doc" xlink:type="arc" />
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWithAugust2010ShorttermNotes_doc" xlink:type="arc" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfWarrantFromDebtModifications" xlink:to="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" xlink:to="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountUponIssuanceOfAugust2010ShorttermNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrent_2_lbl" xml:lang="en-US">Assets, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Assets_2_lbl" xml:lang="en-US">Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrent_2_lbl" xml:lang="en-US">Liabilities, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrent_2_lbl" xml:lang="en-US">Liabilities, Noncurrent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Liabilities_2_lbl" xml:lang="en-US">Liabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquity_4_lbl" xml:lang="en-US">Stockholders' Equity Attributable to Parent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xml:lang="en-US">Liabilities and Equity</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_3_lbl" xml:lang="en-US">ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_3_lbl" xml:lang="en-US">LossOnEarlyExtinguishmentOfDebt</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_2_lbl" xml:lang="en-US">Increase (Decrease) in Accounts Receivable</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xml:lang="en-US">Increase (Decrease) in Deposit Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_2_lbl" xml:lang="en-US">Increase (Decrease) in Deferred Revenue</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_2_lbl" xml:lang="en-US">Repayments of Long-term Capital Lease Obligations</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfNotesPayable" xlink:to="us-gaap_RepaymentsOfNotesPayable_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfNotesPayable_2_lbl" xml:lang="en-US">Repayments of Notes Payable</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Financing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xml:lang="en-US">Cash and Cash Equivalents, Period Increase (Decrease)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsIncurred" xlink:to="us-gaap_CapitalLeaseObligationsIncurred_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsIncurred_2_lbl" xml:lang="en-US">Capital Lease Obligations Incurred</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockholdersEquityForPreferredStock_4_lbl" xml:lang="en-US">StockholdersEquityForPreferredStock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesIssuedForPreferredStock_4_lbl" xml:lang="en-US">SharesIssuedForPreferredStock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharesIssued_3_lbl" xml:lang="en-US">Shares, Issued</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_2_lbl" xml:lang="en-US">Basis of Accounting, Policy [Policy Text Block]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_2_lbl" xml:lang="en-US">Property, Plant and Equipment, Policy [Policy Text Block]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpensePolicy" xlink:to="us-gaap_ResearchAndDevelopmentExpensePolicy_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy_2_lbl" xml:lang="en-US">Research and Development Expense, Policy [Policy Text Block]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxPolicyTextBlock" xlink:to="us-gaap_IncomeTaxPolicyTextBlock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_2_lbl" xml:lang="en-US">Income Tax, Policy [Policy Text Block]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_2_lbl" xml:lang="en-US">Schedule of Accrued Liabilities [Table Text Block]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock" xlink:to="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock_3_lbl" xml:lang="en-US">ConvertiblePromissoryNotesAndOtherNotesPayableTableTextBlock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" xlink:to="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_2_lbl" xml:lang="en-US">ScheduleofSharebasedCompensationExpenseTextBlock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareAbstract_2_lbl" xml:lang="en-US">Earnings Per Share [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_2_lbl" xml:lang="en-US">Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_2_lbl" xml:lang="en-US">Accrued Liabilities, Current [Abstract]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentCarryingAmount" xlink:to="us-gaap_DebtInstrumentCarryingAmount_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentCarryingAmount_2_lbl" xml:lang="en-US">Long-term Debt, Gross</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsExpectedVolatilityRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate_2_lbl" xml:lang="en-US">Fair Value Assumptions, Expected Volatility Rate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2_lbl" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_2_lbl" xml:lang="en-US">Common Stock, Capital Shares Reserved for Future Issuance</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectiveIncomeTaxRateReconciliationOther" xlink:to="VSTA_EffectiveIncomeTaxRateReconciliationOther_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectiveIncomeTaxRateReconciliationOther_2_lbl" xml:lang="en-US">EffectiveIncomeTaxRateReconciliationOther</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:to="us-gaap_TemporaryEquityRedemptionPricePerShare_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare_2_lbl" xml:lang="en-US">Temporary Equity, Redemption Price Per Share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsRiskFreeInterestRates" xlink:to="VSTA_FairValueAssumptionsRiskFreeInterestRates_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueAssumptionsRiskFreeInterestRates_2_lbl" xml:lang="en-US">FairValueAssumptionsRiskFreeInterestRates</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_2_lbl" xml:lang="en-US">ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_3_lbl" xlink:type="arc" />
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